RootkitRevealer is an advanced root kit detection utility. It
output lists Registry and file system API discrepancies that may
indicate the presence of a user-mode or kernel-mode rootkit.
RootkitRevealer successfully detects all persistent rootkits
published at www.rootkit.com, including AFX, Vanquish and
HackerDefender (note: RootkitRevealer is not intended to detect
rootkits like Fu that don't attempt to hide their files or registry
keys).
Download it from here