Not true. Very not true. What do you know? I mean, what is unquestionably true? Math? Basic arithmetic is unprovable, and all other math is based on the assumptions made in arithmetic. Logic? another bunch of assumptions. You assume that if a then b; a. Therefore b. You can't prove that because it's one of the base assumption. There's nothing below it to use to prove it. God? Let's not go there.
It's impossible to prove anything false. It's even harder to prove it true.

But, I don't know this for sure.

"There are no facts, only interpretations." -- Friedrich Nietzsche

FatAlbertTheta: I, too, like the definition of "know" being simply that you don't doubt it, but the strict definition is somethign you're certain of that is true. Either way, knowledge is possible, but unreasonable, IMO.