If you're having problems with LSASS.EXE then please read the informations about the worm "W32/Sasser":
http://vil.nai.com/vil/content/v_125007.htm
In this context you could find avserve.exe on your system, too!
Do a Norton Scan Online
Go to this page and click on Scan for Viruses
http://security.symantec.com/ssc/vc_...KVYRMHCGVRVRMN
It needs to download a few file so as to activate the scan so you may see a message like this.
"The Scan for Viruses uses an ActiveX program to scan your computer. The download is approximately 1.5MB and can take about 10 minutes over a 28.8 modem.
The scan can take more than 20 minutes depending on the speed of your computer and the number of files that you have. Please do not browse away from this page unless you intend to abort the scan.
Downloading Scan for Viruses controls. Please wait...
During the download, you might see one or more messages asking if it is OK to download and run these programs. Click Yes when these messages appear.
Note: Scan for Viruses does not scan compressed files"