If viruses, trojan horses, worms, SPAM, spyware, adware, identity theft, and all the other security issues that we need to worry about are not bad enough. Now, it appears that 'Rootkit' attacks may be on the rise. Rootkits are nothing new, and have been around for years.
SecuritySearch.com defines a 'rootkit' as: "a collection of tools (programs) that a hacker uses to mask intrusion and obtain administrator-level access to a computer or computer network. The intruder installs a rootkit on a computer after first obtaining user-level access, either by exploiting a known vulnerability or cracking a password. The rootkit then collects userids and passwords to other machines on the network, thus giving the hacker root or privileged access."
Rootkits are generally hard to detect, they're designed that way. Well now, Rootkits are being designed to be even harder to detect. This article goes into more detail about the subject.