If your computer is experiencing the issue that system guard disabled frequently, and you are unable resolve it permanently by clicking the Fix button, continue to the solutions below.
1. Click Start, Run, type Explorer.exe, and click OK.
2. Navigate to C:\Documents and Settings\All Users\Application Data\McAfee\HackerWatch\data.
3. Delete the file HwLocal.xdb.
4. Close Windows Explorer and restart your computer.
5. Right-click the M icon in the system tray (near the clock) and select Updates.
And since you state that your computer got infected, after updating mcafee run a full scan to ensure no threats are detected.
After following these instructions, a full scan returned no viruses. However, by the time the scan was completed the McAfee was reporting "unable to verify subscription" for all four areas of the Protection Status screen. Clicking on the "Fix" button returns a message "One or more problems requires attention." Clicking on the link to "verify subscription now" yields a message "unable to verify subscription, if condition persists, reinstall McAfee."
The subscription expiration date at the bottom of the screen reports "no data available."
At this point, McAfee appears completely disabled.
Help is requested.
Prompts from McAfee SecurityCenter requesting that you verify your subscription can have many causes, including issues with your Internet connection or computer settings. To troubleshoot and resolve these issues, please follow the steps below in order.
http://service.mcafee.com/faqdocument.aspx?id=TS100762&lang=en_US&prior_tid=2&An swerID=16777217&turl==http%3A%2F%2Fkb.mcafee.com%2Finfocenter%2Findex%3Fpage%3Dc ontent%26id%3DTS100762%26actp%3Dsearch