Whilst googling for something at work earlier, I ended up on a site which had obviously been a little bit, er, compromised (as this has nothing to do with whatever postgreSQL weirdness I was hunting for).
Anyway, I'm lazy so I'll just cut-and-paste what I wrote in an email about it at the time:
oh no, 'windows security center' on some utterly random website has
detected that I have a virus! And that I have no anti-virus
software... gosh, I'd better install this one that it's helpfully
suggesting to me. I do hope it will run on linux!
Clearly a fake scammy website, and indeed this sort of thing has been in the news recently as well.
Anyway, this one particularly annoyed me, because I couldn't get away from it. Clicking 'cancel' generated another alert "strongly suggesting" that I install it, and the only way out of that was to click ok and have the download dialog pop up. But that's ok, I'll just cancel it (or run it in wine for a laugh). Only no, can't do that, because the original alert has popped up again, and until that goes away I can't click anything else....