Corporate users of some Symantec antivirus product are facing persistent attacks that target a vulnerability that the security provider patched more than seven months ago.

The attacks are yet more proof that IT professionals, not just mom and pops running their first PC, are dangerously lax about installing crucial security patches. The exploits turn user PCs into zombies that spew spam and carry out nefarious acts, such as denial of service attacks. The attack targets unpatched versions of Symantec Client Security and Symantec AntiVirus Corporate Edition, according to CNET.

New variants of the worm that target the vulnerability surfaced in mid December and are proving more effective than previous ones, a senior director of Symantec said. Symantec had initially dismissed the flaw, saying it wasn't likely to be exploited, until the first version of the worm surfaced in November.

Unlike many Symantec updates, which are installed automatically, the fix for corporate antivirus software has to be downloaded on the company's website and manually installed. Symantec is re-evaluating this policy.

The company plans to push a definition to antivirus users that will allow the software to more precisely pinpoint the worm. ®