The term "rootkit" is a difficult one to define, or at least fix a definition on.  Originally it referred to a script, set of scripts, or package of modified system programs (thus "kit") used for gaining or keeping unauthorized root permissions (or equivalent supervisory powers) on a compromised system. Recently, media usage has expanded this definition to include any software that can hide software or processes on a system, but this usage is vague and likely to lead to confusion.

Antirootkit.com doesn't have an awful lot of information on the site, but it does have a list of rootkit detection software.  There are brief descriptions of the products.  Be careful of the download links: they can be misleading in terms of what you are actually getting.

Sophos has always been a solid antivirus company, so there is no reason to think that their anti-rootkit product is any less.

GMER is a Polish anti-rootkit program (Windows only) available for free download.

McAfee Rootkit Detective (originally from Avert) is available for download, but the McAfee site makes sure you know it is a beta product, and requires knowledgeable application and use.

Panda tends to oversell their products, but their anti-rootkit is also available for download.

As usual with most Trend Micro products, RootkitBuster sounds fairly agressive.

F-Secure's BlackLight Rootkit Elimination Technology is well-regarded in the anti-malware research community.  It is available in their complete product, but can also be downloaded separately as a utility.  F-Secure also provides a little bit of rootkit explanation.




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