Security researcher Brian Krebs gets sent some pretty weird stuff from fans. His latest in bizarre snail mail booty: A packet full of fake cash.

Krebs was given four fake $100 bills and two fake $50 bills. He doesn't know who sent them, but spent time examining them to illustrate what some pretty decent (but still, of course, highly illegal) fake money looks like. While they're fairly convincing if you're just taking a quick glance, Krebs pointed out that they aren't able to pass an ultraviolet light test. He found other fairly obvious discrepancies, as well.

Krebs' breakdown of why the fake money is fake is a disconcerting reminder that we might be passing around bogus bills... some of the tests he did required a microscope to confirm that the bills were bullshit, and it's not like your check-out guy at the bodega is whipping one out every time he gives you change. Fake money persists not because it's necessarily good, but because it's good enough. [Krebs On Security via BoingBoing]