Are you using browser extensions?

[hazelnut]

Have a read of this, it will make you think hard about what extensions you use.

https://krebsonsecurity.com/2021/03/is-your-browser-extension-a-botnet-backdoor/

[Dave CCleaner]

Case in point: A video downloader for Facebook and Instagram photo downloader with malicious intent https://decoded.avast.io/janvojtesek/backdoored-browser-extensions-hid-malicious-traffic-in-analytics-requests/ (technical analysis).

This is one of the reasons why CCleaner Browser is a little more resistant to random browser extension installation.

While CCleaner itself does not currently do reputational analysis on browser extensions, it does have a handy tool to review what plugins you currently have installed (Tools > Browser Plugins).  We'd recommend removing anything that you may have loaded up a while ago and aren't using.  CCleaner gives you a quick way to review, disable or delete browser extensions all in the one place -  or you can do it manually the slow way as per https://www.ccleaner.com/knowledge/how-to-disable-or-remove-browser-extensions

 

[Andavari]

Some nefarious variety could likely be used for mining. If antivirus is not detecting anything one way to sort of know something is going on is if the browser is using too many resources in the background for no apparent reason like when only one tab is open.