Hum... unfortunately US100 dollar bills are the world's most counterfeited notes, because of too many reasons.
Obviously we know that there are still many countries that still accept payments in USD, which many tourists sure will be more than happy to use, but you know, there are always evil things going on...
Leaving that aside, the security of the US note honestly in my opinion is a laughing stock. Metallic thread, ink, and watermark would most certainly would be the obvious security features, but other than that, it is not too horribly hard to counterfeit the rest of the other features! But honestly, how often would an average Joe look at the security feature of a banknote in a daily transaction? The worst story I heard this month is that some person tried to withdraw some $8,000 in China *FROM A BANK* all in 100 dollar bills and shockingly, over 40% of his bills are counterfeit. (lol) (obviously, he lost quite a fair bit of money there)
But yes, I was just disappointed that the 20 dollar hologram design didn't make it, or it would have been a great way to ward off such counterfeit banknotes that still circulate...