Q. What is a Rootkit?

A rootkit is a persistent virus that is much harder to remove than a normal virus because it gains privileged access to the machine, modifies the system at a low level and cloaks its visibility. Once established, rootkit infections often evade normal antivirus scans.

The first line of defense against rootkits is to never install any software that you don’t know that the source is reputable. The classic mode of infection is to download a movie or other internet content, and get a popup saying that you need to install a player or a ‘codec’ before you can watch the materials.  When you grant permission for the software to install, you are permitting the rootkit full access to infect and modify your machine.

The term rootkit is usually understood to mean malware – Sony infamously deployed a rootkit as a copy protection to prevent some Sony published audio CDs from being copied to a computer digitally. Sony met some severe backlash from consumers and was forced to withdraw the copy protection and settle with the Federal Trade Commission in the USA.

One family of rootkit malware results in Google and Yahoo search links being redirected to different websites than you intended.

Anti-Rootkit tools
Sophos: http://www.sophos.com/products/free-tools/sophos-anti-rootkit.html
GMER: http://www.gmer.net/
TDSSKiller: http://support.kaspersky.com/viruses/solutions?qid=208280684