If you&8217;ve used a PC for any length of time, you likely remember when the biggest security threats came from downloaded applications. Viruses, trojans, and spyware lurked in cracked software or shady installers. Today, much of our work and play happens inside a web browser, but the same caution applies&8212;especially to the small add-ons known as browser extensions.

Yet many users remain unaware of the risks. In recent months, several people told me they wanted a new feature in Chrome and planned to install the first extension they found in the Chrome Web Store, without checking its developer or permissions. One assumed extensions were created by Google itself. Another believed every listing was thoroughly vetted and trustworthy. Both were surprised to learn that malicious extensions exist and can be programmed to spy on users.

How browser extensions work

To understand the danger, you need to know what an extension actually is. Browser extensions are small pieces of software that run inside your browser&8217;s environment. They have their own application programming interface (API), a tiny storage allocation, and what amounts to a mini registry. The browser acts as a barrier, isolating extensions from raw memory, the file system, and other applications. In theory, an extension should only be able to interact with the web page you&8217;re viewing, based on the permissions you grant.

But theory and practice don&8217;t always align. Browser code can be flawed, and attackers find ways to escape the sandbox. Once an extension breaks out of its confines, it can access your PC&8217;s broader resources: reading your passwords, scanning your files, capturing keystrokes, or even installing additional malware.

Expert insight: Mike Danseglio on extension risks

For a deeper look, I spoke with Mike Danseglio, an ethical hacker and cybersecurity instructor who regularly attends Def Con, the world&8217;s largest hacker conference. He previously worked at Microsoft on Windows security features. His perspective is sobering.

“Browser extensions are strange little beasts,” Danseglio told me. “They really are little apps that live in the browser&8212;they have their own API, mini storage allocation, tiny registry, etc. They are typically isolated from raw memory/filesystem/other-app access by the browser itself acting as a barrier. There have been exploits where an extension &8216;escapes&8217; its browser-imposed boundaries and accesses other stuff, like the file system or raw memory to steal data.”

He adds: “Ultimately, this is the way I look at it: A browser extension is software, like any other. I assume all browser extensions can communicate with other apps, access memory, and do whatever a standalone app can do. So I&8217;m just as careful installing and using a browser extension as I am with any other app.”

Real-world dangers: Malicious and hijacked extensions

Malicious extensions are not hypothetical. Over the years, researchers have uncovered thousands of dangerous add-ons in the Chrome Web Store and Mozilla&8217;s add-on marketplace. Some masquerade as useful tools&8212;ad blockers, coupon finders, grammar checkers&8212;while secretly harvesting browsing history, login credentials, or credit card numbers. Others display unwanted ads or redirect searches to affiliate sites.

A particularly insidious threat is the hijacking of legitimate extensions. A developer may sell their popular extension to a new owner, or an attacker may compromise the developer&8217;s account. The extension then receives a seemingly routine update that includes malicious code. Users who downloaded it months ago no longer have a reason to distrust it, but suddenly their browser is compromised. This has happened to well-known extensions with hundreds of thousands of users.

Browser makers do try to remove harmful add-ons, but detection is not instantaneous. Google, Microsoft, and Mozilla rely on automated scanning, user reports, and sometimes external research to identify threats. By the time a malicious extension is pulled, it may have already affected thousands of users.

How to protect yourself

Given these risks, what steps can you take? The most effective approach is to minimize the number of extensions you install. Think carefully before adding each one. Ask yourself: Do I really need this functionality? Is there a built-in browser feature that does the same thing? For example, Chrome&8217;s built-in password manager may eliminate the need for a third-party password extension.

When you do install an extension, only use the official store for your browser. Avoid sideloading extensions from random websites. Check the developer&8217;s name and see if they have a website or a history of trustworthy apps. Read reviews from independent tech publications&8212;not just user ratings, which can be faked. Look at the number of downloads: an extension with millions of users is more likely to be legitimate, but not guaranteed.

Examine the permissions the extension requests. A simple timer or note-taking extension should not need access to all websites or your browsing history. If a permission seems excessive, consider finding an alternative. Many users grant permissions without reading, which is exactly what malicious developers count on.

Regular auditing and removal

It&8217;s also important to periodically review your installed extensions. Go through the list in your browser&8217;s settings and uninstall anything you no longer use. Even if you haven&8217;t opened an extension in months, it can still run in the background and access your data. Keeping only the essentials reduces your attack surface.

Some security experts recommend disabling extensions by default and enabling them only when needed. Chrome and Firefox both allow you to toggle individual extensions on and off. This is tedious for frequently used tools, but for occasional use add-ons it can prevent background activity.

Finally, consider using a separate browser profile for sensitive tasks like online banking or shopping. Keep that profile free of all extensions. If a malicious tool is lurking in your main browser, it won&8217;t be able to intercept your financial transactions.

The only way to guarantee an extension cannot spy on you is to never install it at all. That&8217;s an extreme stance, but it reflects the reality that every piece of software adds risk. By being selective and vigilant, you can enjoy the convenience of browser extensions without becoming the next victim of a data-stealing add-on.

Source: PCWorld News