I was browsing SuperUser.com looking for a way to fix Widnows (Tantalus level effort, but still), and I noticed a duck asking me if it could help me.
My first thought was that my browser was infected!
However, after a little bit of searching, apparently it's an April Fools prank. I eventually came across questions on various meta boards (physics, meta, meta April Fools) explaining it was an SE-wide phenomenon.
OK, so now I know that my browser is not infected. How should I, or could I, have known it was a prank and not an infection if I could not have found other people asking about it?