What Is Malvertising? Protect Your Business from Malicious Ads

Advertising is everywhere; scroll through social media, read a news article, or watch a video, and you’ll likely encounter multiple digital ads. If you run a business online, chances are you’re using some form of advertising to reach your audience, too. But what if those very ads meant to grow your brand could actually harm it?

Malvertising (malicious advertising) is a relatively new cyberattack technique that hides malicious code within seemingly legitimate online advertisements. These infected ads are often distributed through trusted advertising networks, making them incredibly difficult to detect for both users and publishers. Once live, they’re served to every website visitor, putting virtually anyone who views the page at risk.

In fact, studies suggest that around 1% of all online advertisements could be hiding malicious code. And with billions of ads run every day, that’s not a small number! But, it’s not just small websites or unknown platforms being targeted, major organisations like The New York Times, BBC, and Spotify have all fallen victim to these stealthy attacks.

In this post, we’ll break down exactly what malvertising is, explore the different types of threats it involves, share real-world examples, and, most importantly, give you practical, actionable steps to help identify, remove, and protect your business from malicious ads.

Defining Malvertising

Put simply, malvertising involves injecting malicious code into digital ads, often without the knowledge of the website hosting them. These ads look and behave like any normal ad, but are quietly working to exploit security gaps. One of the most alarming aspects is that some attacks don’t even require a click. Through what’s known as a drive-by download, the malicious code can run as soon as the ad is loaded in a user’s browser

Key Characteristics of Malvertising Include:

Stealthy and silent: Malicious code runs quietly in the background, making detection difficult.
Delivered through trusted networks: Even legitimate ad networks can unknowingly distribute these harmful ads.
Pre-click execution: Users don’t need to click for the malware to activate.
Exploits browser and plugin vulnerabilities: Especially those in outdated or unpatched software like Adobe Flash or Java.

Malvertising typically follows this five-stage process:

Creation of malicious ads: Cybercriminals design attractive advertisements using legitimate logos and branding to avoid raising suspicion.
Infiltration of ad networks: Attackers pose as legitimate advertisers to submit their malicious content through reputable ad networks.
Delivery through trusted websites: When users visit infected sites, the malicious code activates without requiring suspicious behaviour from the site itself.
Execution via user interaction or drive-by download: Malware activates either through clicking (post-click attack) or simply viewing the ad (pre-click attack).
Monetisation through data theft or ransomware: Attackers profit by selling stolen data on dark web marketplaces or demanding ransom payments to restore encrypted files.

The interconnected nature of online advertising makes defending against these threats particularly challenging. Ad networks serve countless advertisements through real-time bidding systems, making thorough testing of every ad nearly impossible.

How It Differs from Traditional Malware and Adware

Unlike traditional malware, which often relies on tricking users into downloading infected files, malvertising uses legitimate websites as delivery systems. It looks real, even to experienced users.

It’s also important not to confuse malvertising with adware. While both involve digital ads, adware is usually installed on a user’s device without consent and shows unwanted ads while collecting data. Malvertising, on the other hand, is deployed remotely through a website’s ad system and only impacts users who visit the compromised webpage.

Once active, the malware delivered through malvertising can do everything from stealing sensitive data and corrupting files to redirecting traffic or creating backdoors into company systems. Some malware acts immediately, while others can lie dormant for months before launching an attack.

Why Even Legitimate Websites Are at Risk

Many reputable websites unknowingly serve malvertising due to the complex and often opaque nature of online advertising. Publishers commonly rely on third-party ad vendors to fill ad spaces, leaving them with little control over what actually gets displayed. With billions of ads served daily, thorough screening of every ad is virtually impossible.

Most ad networks use a complaint-based system, only reviewing ads after users report something suspicious. By then, damage is often already done.

The Business Impact of Malvertising Attacks

Malvertising can be a serious business risk. Many businesses rely on mobile devices, computers, and other technology to manage systems, store sensitive data, communicate with clients, and drive daily operations. Plus, remote work and the growing trend of BYOD (bring-your-own-device) mean that employees are browsing and accessing company resources from a wide range of devices and networks, many of which may not be adequately secured. This creates more entry points for malicious ads to slip through and compromise your business.

Financial Losses

Whether it’s dealing with cleanup costs, lost ad revenue, or system downtime, malvertising can come with a hefty price tag. Businesses may need to invest in digital forensics, IT support, or new cybersecurity infrastructure to recover from an attack.

Data Breaches & Legal Consequences

Many malvertising campaigns aim to steal sensitive data, customer records, payment details, login credentials, and more. A successful breach doesn’t just impact your users; it can trigger legal obligations, especially if you’re handling regulated data under laws like the Privacy Act (Australia), GDPR (EU), or CCPA (US). The costs of legal counsel, regulatory fines, and compensation for affected customers can be overwhelming.

Loss of Trust & Damage to Reputation

Trust takes years to build, but seconds to lose. If customers associate your brand with a security issue, it can erode confidence and loyalty. Even if the malicious ads didn’t originate from your business directly, being the platform where users were infected can still damage your reputation. This impact can extend to partnerships, investor relationships, and your standing in the wider industry.

How Malvertising Works

The online advertising ecosystem creates perfect conditions for malvertising due to its complex, multi-layered structure. Every ad you see involves a sophisticated network of publishers, ad exchanges, servers, and content delivery networks, each of which represents potential entry points for attackers.

Attackers take advantage of this complexity through several technical methods. First, they infiltrate legitimate ad networks by either posing as ordinary advertisers or compromising existing advertising accounts. Once inside, they inject malicious code into seemingly harmless advertisements that later appear on trusted websites.

Redirection techniques are what make malvertising particularly effective. When an infected ad loads, it often triggers a series of redirects through multiple URLs before reaching the final malicious destination. These redirections typically use HTTP 302 requests, which indicate content has temporarily moved to another location. Sometimes attackers use JavaScript methods like location.replace that leave no trace in browser history, effectively hiding the redirection from users.

The actual infection usually happens through one of two primary methods:

Post-click attacks: These require user interaction, such as clicking on a deceptive ad that looks legitimate but installs malware.
Pre-click attacks: More dangerous “drive-by downloads” that execute automatically when a page loads, without requiring any user action.

During execution, malvertising typically uses exploit kits – tools that automatically scan devices for security vulnerabilities in browsers, plugins, or operating systems. These kits target outdated software like Adobe Flash, Java Runtime Environment, or other browser components. Once they identify vulnerabilities, the exploit kit delivers a customised malware payload designed specifically for the detected weakness.

Ad networks process billions of submissions daily, making a thorough security analysis of each ad virtually impossible. Additionally, malicious code is often obfuscated, deliberately written to appear harmless while hiding its true purpose from security scanners.

As a result, even premium publishers with strong security measures can unknowingly distribute malicious ads, as the malware operates entirely within the legitimate advertising infrastructure rather than attacking the website itself.

Types of Malvertising Campaigns

There are several unique types of malvertising techniques that compromise devices and steal sensitive data. Each method targets different vulnerabilities using unique attack vectors.

Redirects and fake landing pages

Malvertising frequently uses redirects to funnel users from legitimate sites to malicious ones. These redirects can occur through multiple URLs before reaching the final destination, often using HTTP 302 requests to mask the process. Some attacks employ JavaScript methods that leave no trace in browser history. Once redirected, users see convincing fake websites designed to mimic trusted brands, banks, or government agencies.

Exploit kits and drive-by downloads

Exploit kits are the most dangerous form of malvertising. These tools automatically scan for vulnerabilities in browsers, plugins, or operating systems. The Angler, Nuclear, Magnitude, and RIG exploit kits commonly appear in malvertising campaigns. These kits power “drive-by downloads” that install malware without any user interaction beyond simply viewing an infected page. This technique silently exploits weaknesses in software like Adobe Flash, Microsoft Silverlight, and Oracle Java.

Fake software updates

Another common tactic shows counterfeit update notifications for browsers, media players, or security software. These deceptive prompts often include countdowns, alert sounds, or security warnings to create urgency. Users who click “Download” or “Update” unknowingly install malware instead of legitimate updates. FakeUpdates malware ranked among the leading malware families in 2023 and is still prevalent today.

Browser lockers and scareware

Browser lockers trap users on a webpage by triggering endless pop-up dialogues or expanding to full-screen mode. Meanwhile, scareware displays alarming false virus warnings with flashing colours and urgent messages like “Virus Detected!” or “Critical Threat!” Both techniques aim to frighten users into calling fake support numbers or purchasing worthless security software. Scareware campaigns jumped 42% month-over-month in fall 2023.

Phishing ads and credential theft

Phishing advertisements collect sensitive information by using attractive offers or imitating the login pages of popular services. These malicious ads lead to fake forms designed to capture credentials, financial data, or personal information. In early December 2024, Microsoft identified a large-scale malvertising campaign that affected nearly one million devices globally through this technique.

Real-World Malvertising Examples

Malvertising is a very real danger that has successfully breached some of the world’s most well-known platforms. If it can happen to them, it can happen to anyone.

Yahoo!

In July 2015, Yahoo was hit by one of the largest malvertising campaigns ever recorded. With nearly 7 billion visits per month, the scale of potential exposure was massive. Cybercriminals used Microsoft Azure-hosted sites to redirect visitors through a layered web of domains, eventually serving them the Angler Exploit Kit. This attack proved particularly effective because it delivered a mix of ad fraud (Bedep) and ransomware (CryptoWall).

Spotify

On March 24, 2011, Spotify’s free-tier desktop users became the target of a Drive-By Download attack. The malicious ad was embedded directly within Spotify’s Windows desktop app and exploited vulnerabilities using the Blackhole Exploit Kit. It secretly installed a rogue program disguised as “Windows Recovery” antivirus software. The bulk of victims were in Sweden (59%) and the UK (40%).

KS Clean

Malvertising isn’t just limited to desktop users. The KS Clean campaign zeroed in on mobile users by disguising a malicious Android app as a helpful cleaning tool. Once installed, the app presented a fake system update screen with only one option: “OK.” This tactic forced users to accept administrator privileges, permissions that couldn’t be revoked afterwards. Over 300 versions of this malware were discovered, mostly targeting users in the US and UK.

How to Identify and Remove Malvertising

Malvertising is designed to look legitimate, which makes it increasingly difficult to detect. But if you know what to look for, you can catch and eliminate these threats before they wreak havoc on your systems. Here’s how to spot suspicious ads, recognise browser red flags, and safely remove potential infections.

Signs of Suspicious Ads

Malicious ads often have subtle (or not-so-subtle) clues that set them apart from the real thing. Watch out for:

Poor visual design: Blurry images, clashing colours, or amateurish layouts often signal something fishy.
Spelling and grammar mistakes: Reputable advertisers proofread; malvertisers often don’t. Typos can be a major red flag.
Urgent or alarming messages: Warnings like “Your computer is infected!” or “Act now to avoid disaster!” are scare tactics meant to trick you.
Unrealistic offers: If it sounds too good to be true, it probably is.
Fake system alerts: Pop-ups that mimic your operating system’s warnings are designed to prompt a quick, unthinking response.

Browser Behaviour to Watch For

Sometimes, it’s your browser, not the ad, that gives away an infection. Keep an eye out for:

Unwanted redirects: Suddenly landing on strange websites without clicking anything is a common symptom.
Homepage changes: If your default homepage or search engine changes unexpectedly, something may be off.
Persistent pop-ups: Annoying ads that won’t go away or keep reappearing, even after you close them.
New, unauthorised extensions: Check your browser settings, plugins you didn’t install could be behind suspicious activity.
Slow performance: A noticeable drop in browsing speed or overall device responsiveness can signal background activity from malicious scripts.

How to Remove Malvertising From Your Browser

If you suspect your device has been hit with malvertising, take action immediately:

Disconnect from the internet: This stops the infection from communicating with its source or downloading more malware.
Run a trusted antivirus scan: Use reputable security software to do a full system scan and remove any threats found.
Clear your browser data: Wipe your cache, cookies, and browsing history to remove any lingering scripts.
Reset browser settings: Revert your browser to its default state to remove malicious changes.
Uninstall suspicious programs: Remove any unfamiliar apps that might have slipped in with the infection.
Update everything: Make sure your browser, plugins, and security tools are fully up to date to patch known vulnerabilities.

⚠️ Tip: If a suspicious pop-up won’t close, don’t click the “X.” Use Task Manager (Windows) or Force Quit (Mac) to shut down your browser completely and safely.

How to Protect Your Business

Malvertising is evolving fast, and so should your defences. But protecting your business requires more than just antivirus software. A truly secure environment is layered and proactive. Here’s how to build your defence strategy:

Use Ad Blockers and Web Filters: Ad blockers serve as your frontline defence by preventing malicious ads from ever reaching your team’s screens. Pair this with web filtering tools that categorise and block access to risky sites, keeping employees away from domains known for hosting malware. Want extra protection? Add DNS filtering. Studies show DNS-layer security could prevent up to one in three cybersecurity incidents by blocking threats before they even reach your network.
Keep Software and Plugins Updated: Cybercriminals love outdated software. It’s an open door to your systems. That’s why it’s critical to regularly update browsers, plugins, operating systems, and any third-party tools your team uses. Turn on automatic updates wherever possible and ensure your IT policies enforce timely patching. Remember, even one unpatched plugin can jeopardise your entire network.
Monitor Network Traffic for Anomalies: Sometimes, the first sign of a breach is a strange data spike or unexpected communication. Network Traffic Analysis (NTA) tools continuously monitor for these anomalies, helping you detect suspicious behaviour, like command-and-control communications or data exfiltration, before it becomes a full-blown breach.
Conduct Regular Security Audits: Security audits keep you one step ahead. By examining your systems, policies, and procedures, you can spot vulnerabilities before cybercriminals do. Prioritise your findings based on risk, and act swiftly to patch weaknesses. A clear remediation plan with deadlines and responsibilities keeps your security roadmap on track.
Train Employees on Safe Browsing: Technology can only go so far; your people are your most important firewall. Since many malvertising attacks rely on social engineering, ongoing employee training is critical. Teach staff how to spot suspicious ads, avoid risky clicks, and report unusual activity. Regular refresher sessions help reinforce good habits and keep cybersecurity top of mind.

Key Takeaways

Malvertising may disguise itself behind polished visuals and legitimate platforms, but its intent is anything but harmless. As digital advertising continues to evolve, malvertising poses a growing threat to businesses of all sizes across every industry.

Understanding what malvertising is and how it works is the first step in protecting your business. From implementing strong technical safeguards to educating your team about suspicious ads and browser behaviours, a proactive, layered approach to cybersecurity can significantly reduce your risk.

Is Your Business Protected Against Malvertising?

Even companies with advanced tools have fallen victim to malvertising attacks. Don’t wait until it’s too late. Get ahead of the threat with a professional security assessment tailored to your business. At CRT Network Solutions help identify vulnerabilities, strengthen your defences, and keep your systems safe.

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