Extensions and add-ons are a great way to get more out of your browser, but they also offer a convenient route for cybercriminals to perform a variety of nefarious acts that could threaten the security of your PC and online activities.

Security firm Avast said this week that it has identified malicious software hidden in at least 28 third-party Google Chrome and Microsoft Edge extensions. Stats from the web stores suggest the extensions have received 3 million downloads globally.

The company said the malware could potentially redirect users to phishing sites, which could lead to an attempt to steal personal data.

The extensions work with popular online platforms such as Facebook, Instagram, Spotify, and Vimeo, and help users download videos and other content from the sites.

“The researchers have identified malicious code in the JavaScript-based extensions that allows the extensions to download further malware onto a user’s PC,” Avast said, adding that users have also reported that the add-ons are manipulating their online experience and redirecting them to other websites.

“The actors also exfiltrate and collect the user’s birth dates, email addresses, and device information, including first sign-in time, last login time, name of the device, operating system, used browser and its version, even IP addresses (which could be used to find the approximate geographical location history of the user),” the security firm noted.

But Avast said the main goal appears to be to monetize the traffic itself, with the perpetrators receiving a payment for every redirection to a third-party domain.

Avast malware researcher Jan Rubín said: “Our hypothesis is that either the extensions were deliberately created with the malware built-in, or the author waited for the extensions to become popular, and then pushed an update containing the malware. It could also be that the author sold the original extensions to someone else after creating them, and then the buyer introduced the malware afterwards.”

Avast’s discovery is an important reminder to always exercise caution when downloading an extension for your browser, and to make sure you have up-to-date antivirus software enabled. Now would also be a good time to review all of your browser extensions and to uninstall those that you rarely use.

Some of the infected extensions are still available for download, though Avast said it’s contacted Microsoft and Google and both companies are now investigating the issue. Browser creators are constantly on the lookout for dodgy extensions. Google, for example, eliminated 500 of them from its Chrome Web Store earlier this year.

Below are the affected extensions discovered by Avast. If you have any of these on your PC, you’re advised to uninstall them immediately and run a scan for malware.

Direct Message for Instagram Direct Message for Instagram DM for Instagram Invisible mode for Instagram Direct Message Downloader for Instagram Instagram Download Video & Image App Phone for Instagram App Phone for Instagram Stories for Instagram Universal Video Downloader Universal Video Downloader Video Downloader for Facebook Video Downloader for Facebook Vimeo Video Downloader Vimeo Video Downloader Volume Controller Zoomer for Instagram and Facebook VK UnBlock. Works fast. Odnoklassniki UnBlock. Works quickly. Upload photo to Instagram Spotify Music Downloader Stories for Instagram Upload photo to Instagram Pretty Kitty, The Cat Pet Video Downloader for YouTube SoundCloud Music Downloader The New York Times News Instagram App with Direct Message DM