Only Symantec's Norton AntiVirus and ESET's NOD32 antivirus caught every variant of the 12 polymorphic families, he said. In that test, OneCare placed 15th, detecting every version of only two families, and missing seven of the polymorphic families completely.

Cleminti's report is available online (download PDF).

This is not the first evaluation to give a Microsoft security program a black eye. Last week, for example, Australian security company PC Tools released research that claimed Windows Defender -- Microsoft's anti-spyware title -- just 46 percent to 53 percent of spyware.

"We are looking closely at the methodology and results of the test to ensure that Windows Live OneCare performs better in future tests," a Microsoft spokesperson said.