Malicios Chrome Extension

So all of a sudden, Chrome got very slow at loading pages, and it even kept disconnecting me from time to time. All that was accompanied with the hard drive rumbling (although the HDD LED wasn't blinking as fast). Then I noticed a message at the bottom of chrome while loading a site: Waiting for Extension O.S . So I went straight to extensions manager, but it kept closing the tab with the extension list as soon as I open it. That got me suspicios and I knew it was a malicios thing. So I managed to quickly scroll to the Extension O.S (description was some gibberish in some other language)and disable and trash it. The moment I did that the Hard drive slowed down. Although my Bitdefender was off for that whole time because I forgot to bring it back on after testing, this is just a warning in case anyone sees a malicios and suspicios extension. Now as a side question, what could that extension have done to me? I mean, what are chrome extension actually permitted to do on a PC? Thank you and take care.