Local Security Authority Subsystem Service (LSASS)^[1] 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.^[2] It also writes to the Windows Security Log.

Forcible termination of lsass.exe will result in the system losing access to any account, including NT AUTHORITY, 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, and the description of the file is Local Security Authority Process. 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.^[3] The Sasser worm spreads by exploiting a buffer overflow in the LSASS on Windows XP and Windows 2000 operating systems.