Local Security Authority Subsystem Service (LSASS) is a process in Microsoft Windows operating systems that is responsible for enforcing the security policy on the system. It verifies users logging on to a Windows computer or server, handles password changes, and creates access tokens.^[1] It also writes to the Windows Security Log.

Forcible termination of lsass.exe will result in the Welcome screen losing its accounts, prompting a restart of the machine.

Because lsass.exe is a crucial system file, its name is often faked by malware.

The lsass.exe file used by Windows is located in the directory %WINDIR%\System32. If it is running from any other location, that lsass.exe is most likely a virus, spyware, trojan or worm. Due to the way some systems display fonts, malicious developers may name the file something like Isass.exe (capital "I" instead of a lowercase "l") in efforts to trick users into installing or executing a malicious file instead of the trusted system file.