Most browser users have no idea what a "session replay" is, or that it is routinely used by a website's owner to analyze user behavior on their site.
Even though Princeton University researchers sounded the alarm about these techniques in November, there has been no real outcry about them that has emerged.
This may be because they do have legitimate uses. Analytics firms such as FullStory, Hotjar, Yandex and Smartlook provide scripts for the site owners to use and then summarize the findings on their analytics consoles.
The use is widespread. In fact, 482 of the Alexa top 50,000 sites are recording their users' every moves, keystrokes and mouse movements with these tools. This includes Yandex, Microsoft, Adobe, GoDaddy, Spotify, WordPress, Reuters, Comcast, TMZ and many others.
While the Metrica script does not record the text that is entered into password fields, it still can still log various sorts of details, such as names, credit card numbers, CVV numbers, email addresses and phone numbers.
In the report, Trend Micro researchers believe that all of these malware extensions were created by the same threat actor, named Droidclub. This is the domain name of the command and control server used to control the extensions.
The Droidclub group relies on "malvertising" to force a landing on a controlled page where social engineering tricks come into play to have the extension get permission to be installed. The extensions will also try to inject ads on everything an infected users sees, which will generate profits for them.
Trend Micro was not able to definitively state how the Yandex script was being used by the attackers, only that they could demonstrate it had the potential to be used to capture personal information.
Droidclub also messes with users trying to uninstall or report the extensions. It will check if the user is visiting a URL where reporting is done -- matching the regular expression https://chrome.google.com/webstore/report/([a-z]+) -- the user is instead redirected to the introduction page of their extension.
If the user tries to remove the extension via Chrome's extension management page -- located at chrome://extensions/ -- the extension will again redirect the user to a fake page, leading the user to believe that the extension has been uninstalled. It hasn't been, and it's still there.
Droidclub's extensions are a nasty piece of work, when one considers how it functions and how it tries to hang on. Fortunately, Trend Micro says CloudFlare Inc. has removed the C&C servers from its service.
— Larry Loeb has written for many of the last century's major "dead tree" computer magazines, having been, among other things, a consulting editor for BYTE magazine and senior editor for the launch of WebWeek.