Your system is heavily damaged by Four virus!
It it absolutely nothing to worry. Feel at ease and close that shitting tab.

There's a special word, or terminology, for this kind of behavior of a random webpage, "scareware". Scaring pages frighten and threaten you by telling you that you're in danger, and try to make you download their promoted software (or even a real virus - though that's rare but that does happen from time to time).

Next time whenever you see something like this, close the tab with confidence. You're in no real danger. It's just a fake page.