I hadn’t been to the Pirate Bay in quite some time. I occasionally pop over to look for old videos. I went today and a big popover for a dubious software upgrade came up. Then, another saying that my system is infected and offering to clean it. That’s obviously fake, but it was blocking my access to the user interface so I wasn’t able to complete my search. Closed it. That’s unfortunate.
Sadly almost all these comments are wrong. I work in a computer shop and we see the scam you’re talking about all the time. It happened because you unknowingly opened an ad. So you clicked on a button that looked legitimate like “download” or “next” or whatever, and that pops up full screen. The fix is a good ad blocker like ublock origin. Google’s being a piece of shit right now about ad blockers so I recommend something Firefox-based for effective ad blocking.