SHA1
broken
cryptographic hash algorithmus
http://www.schneier.com/blog/archives/2006/09/notes_from_the.html
It's even possible to find meaningful messages with identical hash code.
http://www.heise-security.co.uk/news/77244
Widely used. Caveats ahead.
You can read "Finding Collisions in the Full SHA-1," by Xiaoyun Wang, Yiqun Lisa Yin, and Hongbo Yu,
here.
see also MD5, SHA256