The laptop was using Norton's Internet Firewall the first time. Mcafee's the 2nd time. Successive tests have been run without it. Basically it appeared that the firewall had no effect, since LimeWire statest that it works around firewalls. Therefore the only way to properly protect the OS in my opinion was to make sure that the AntiVirus was up to date.

Thanks for reminding of one repair method. In one instance I actually pulled the HD and replaced lsass.exe and repaired the registry through USB. 2 days later lsass.exe was trashed again.