> the treasury department won't tell you what security measures are on the bill, nor when they change them

Here are a few Treasury Department webpages telling you what security measures are on the bill, and they publish a press release with a new interactive site when they change them:

http://www.newmoney.gov/newmoney/flash/interactive100/index....

http://www.newmoney.gov/uscurrency/redesigned100.htm

http://www.moneyfactory.gov/anticounterfeiting/securityfeatu...