NAV 2011 says all is fine, but my gut says a virus is affecting Lsass.exe

Dear Norton Community,

 

A few signs make me suspect I have a virus: 1) NAV 2011 warned me a week ago that my default browser* was using lots of system resources. 2) Yesterday, NAV warned me that Lsass.exe was using lots of CPU and was both reading from and writing to the hard disk. A few moments later, NAV stopped responding. 3) Even after one or two reboots, everything seems to be running just a little more slowly. The computer freezes up for a moment or two. None of this was happening 2 weeks ago.

 

Despite all of this, NAV and Norton Power Eraser tell me everything is fine.

 

Is there anything else I can do to gain extra peace of mind that everything really is fine--and maybe get my computer to start performing the way it was doing 2 week ago? If doing a complete reinstallation of Vista would help, this wouldn't be too much of a headache.

 

 

Background info:

 

  • NAV 2011, with definitions updated a few mins ago.
  • I ran a full NAV scan. Just in case I was missing any rootkits, I also used Norton Power Eraser. Both programs say everything is fine.
  • Windows Vista, 32-bit version - checked for updates a few mins ago
  • Default browser: Safari. I also use Chrome, Firefox 4, and sometimes Opera or IE9.

 

Thanks very much for any advice,
Jon