I have been having problems with this exe taking up a lot of CPU usage, and when it is active my PC grinds to a halt. Is this a necessary application? I cannot end it as it says it is a critical system operation, but I have heard that a Trojan disguised as lsass.exe exists. I have an upto date AVG which scans every night and has found nothng. How can I tell if the lsass.exe is the real thing or a possible trojan?