Malicious Browser Extensions and Adware

 

You install a browser extension to block ads or manage passwords, but without knowing it, you’ve handed over your browsing history, login credentials, or even full system control to a cybercriminal. This is the danger posed by malicious browser extensions and adware—some of the most underestimated security threats in today’s digital landscape.

According to cybersecurity firm Kaspersky, over 4 million users were affected by malicious browser extensions in 2024 alone, with attackers using them to inject ads, steal data, and hijack browser settings.

In this guide, we’ll explore:

• What malicious extensions and adware are

• How they infect your system

• What damage they can cause

• Red flags to look for

• How to remove them

• Proactive defenses to stay protected

What Are Malicious Browser Extensions?

Browser extensions are small software programs that customize your browsing experience. While most are safe and useful, some are designed with malicious intent or become dangerous after a rogue update.

These malicious extensions can:

• Monitor your online activities

• Steal passwords and credit card data

• Redirect search results to fake sites

• Inject advertisements or trackers

• Download additional malware

• Exploit browser permissions

⚠️ Common disguises:

• “Free PDF Converter”

• “Ad Blocker Premium”

• “Price Comparison Helper”

• “Dark Mode Enhancer”

These often promise utility but include hidden data-mining or spyware functionality.

What Is Adware?

Adware is software that automatically displays or downloads advertising material—usually in the form of pop-ups, banners, or auto-redirects. While not always dangerous, many forms of adware are malicious, slowing down systems and compromising user privacy.

Some adware:

• Tracks your searches and sells the data

• Opens backdoors to more dangerous malware

• Installs itself without clear user consent

• Makes it difficult to uninstall

🔍 Adware can appear as:

• Fake “system cleaners”

• Bundled software in freeware downloads

• Browser hijackers that change your homepage/search engine

How Do These Threats Infect Your Browser?

✅ 1. Through the Chrome or Firefox Web Store

Even legitimate-looking stores are not foolproof. Some extensions sneak in and are later updated with malicious code once installed by thousands.

🧑‍💻 2. Bundled with Free Software

A common tactic is to hide extensions or adware in:

• Free video downloaders

• Pirated software

• Games and utilities from unknown sources

If you rush installation and click “Next” blindly, you might give consent to install a hijacker.

📧 3. Phishing Emails or Fake Websites

Clicking “Install Extension” from a sketchy email or a fake browser warning (“Your browser is outdated!”) can infect your system instantly.

💾 4. Drive-by Downloads

Some websites exploit browser vulnerabilities to install malicious extensions or adware without your explicit permission.

What Can Malicious Extensions and Adware Do?

💣 1. Hijack Search Engines and Homepages

Your default search engine suddenly changes to something like search4you.biz or mybestsearch.net? That’s adware at work.

📡 2. Track Every Website You Visit

Many extensions request permission to “Read and change all your data on the websites you visit.” This allows them to:

• Log every click

• Capture form data (including login info)

• Spy on your private activity

🔐 3. Steal Credentials or Payment Info

Some rogue extensions are built solely to mimic password managers or autofill tools to capture your sensitive data.

🧠 4. Insert Fake Ads or Redirects

They modify websites you visit—injecting banners or redirecting links so that they get affiliate revenue or scam you directly.

🧳 5. Download More Malware

One malicious extension can act as a delivery system, quietly downloading trojans, spyware, or ransomware onto your machine.

Red Flags That You Have a Malicious Extension or Adware

Here are clear signs something is wrong:

🚩 1. Your Homepage or Search Engine Changes

You didn’t ask for it, but now you’re using a weird search provider.

🚩 2. Unwanted Ads Everywhere

Banner ads, pop-ups, video ads—often unrelated to the websites you’re on.

🚩 3. Slow Browser Performance

Extensions running in the background may be using your browser to mine cryptocurrency or send data.

🚩 4. Extensions You Didn’t Install

Check your extension list—anything unfamiliar could be dangerous.

🚩 5. Redirects or Search Hijacks

Clicking a link takes you somewhere you didn’t expect—often to low-quality or suspicious domains.

🚩 6. Warnings from Antivirus Software

Modern antivirus tools often detect known rogue extensions.

How to Check and Remove Malicious Extensions

🧼 Step-by-Step for Chrome:

1. Go to chrome://extensions

2. Review all installed extensions

3. Remove anything you don’t recognize or didn’t install

4. Use Chrome Cleanup Tool or a trusted antivirus scanner

🔍 Step-by-Step for Firefox:

1. Go to the menu > Add-ons and Themes

2. Check Extensions tab

3. Disable or remove unknown or suspicious ones

4. Use tools like Malwarebytes to double-check

💡 Tip:

If you're unsure about an extension, Google its name + “malware” or “scam” to see if others have flagged it.

How to Remove Adware from Your Computer

1. Uninstall Suspicious Programs via your Control Panel or Applications folder

2. Reset Your Browser Settings

   • Chrome: Settings > Reset and clean up > Restore settings to their original defaults

3. Run Full Malware Scans using trusted tools like:

   • Malwarebytes

   • Bitdefender

   • Windows Defender

4. Clear Your Cache and Cookies to eliminate hidden scripts or trackers

How to Prevent Future Infections

🔒 1. Be Cautious with Permissions

Don’t install extensions that ask for excessive access unless absolutely necessary.

🔐 Pro Tip: Legitimate extensions usually require only minimal permissions. If one wants to "read and change everything on all websites," think twice.

🛍 2. Stick to Official Extension Stores

Even then, check reviews, developer name, number of users, and last update date.

📅 3. Regularly Audit Your Extensions

Review your browser extensions monthly—remove anything you don’t use.

🧰 4. Use a Trusted Antivirus Suite

Modern antivirus software like Norton, Kaspersky, or Bitdefender can detect extension-based threats in real time.

🧠 5. Educate Everyone on Your Network

If you manage an office or home network, make sure all users understand the risks of installing rogue extensions or clicking suspicious ads.

Examples of Known Malicious Extensions

Over the years, even major browsers have hosted dangerous extensions like:

Extension Name	Behavior
"HD Video Converter"	Injected affiliate links and redirected searches
"PDF Converter Elite"	Collected browsing data and sold to third parties
"AdBlock Plus (Fake Clone)"	Lookalike scam that installed adware
"Weather Forecast Extension"	Monitored keystrokes and passwords

Even extensions with 100,000+ users can go rogue after being sold to shady developers, which has happened in multiple high-profile cases.

Closing Thoughts: Your Browser Is Your Front Line

If your browser is compromised, everything you do online is compromised too.

That’s why you need to treat browser extensions with the same caution as any app you download. With a little vigilance and the right tools, you can keep malicious extensions and adware out of your digital life—for good.