Half of the rootkits tested against anti-virus suites and online scanners prove tough to catch. No real surprise there...

New Tests Show Rootkits Still Evade AV - Dark Reading

The XP test used 30 active rootkits and 30 pieces of malware using rootkit technologies. Not surprisingly, anti-rootkit tools did the best, detecting about 80 percent of the rootkits overall, while the security suites found over 66 percent, and online scanners, only 53 percent. Some tools crashed or hung up after completing the rootkit scans, and those were counted as “not detected.”

Security suites did better detecting inactive rootkits than active ones -- most found all (or nearly all) 30. But detecting and cleaning up active rootkits -- which is the task that AV-Test.org considers the “real rootkit test” -- was another story.
via Slashdot