Gmer, a popular rootkit detection software, has been unavailable for download since some time in December, 2006. It appears that the rootkit scumware writers found the software too effective. The server hosting Gmer has been under a heavy and violent DDoS attack that successfully and completely blocked access to the download site. The host has deactivated the domain.
Other mirrors quickly underwent the same attack and had to remove the download. However, as Marco Giuliani reported, Gmer is available for download at MajorGeeks and here.