The latest security tests from Virus Bulletin have identified 19 of the 54 security suites examined as inadequate for VB100 status.
The products were tested on Windows Vista Business Edition SP2 using a variety of malware and security simulations, and the testers noted a marked inability of some software to cope with heavy attacks.
"Most notable this month has been the remarkable level of instability under pressure in many of the products," said John Hawes, Virus Bulletin's anti-malware test director.
"While our tests do put unusual strain on products, it is clearly important that security software should continue to function under pressure, and should not crumble in the face of heavy attack. Flaky behaviour will certainly not instil a sense of security in users."
The team also noted very high false positive rates, and that legitimate files from Corel, Roxio and Adobe were falsely identified as being infected. Kingsoft and Bkis BKAV scored particularly poorly, but Microsoft's free security suite did pass the VB100 test.
"The most important validation of anti-virus quality comes from independent certification organisations like Virus Bulletin," said Eric Foster, group manager for Microsoft Windows marketing.
"It is no surprise that we are very excited that Microsoft Security Essentials achieved the VB100 award."
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