The process lsass.exe serves as the Local Security Authentication Server by Microsoft, Inc. It is responsible for the enforcement of the security policy within the operating system. This process checks whether a user’s supplied identification is valid or not whenever he or she tries to access the computer system.
With the execution of the file lsass.exe, the system acquires security by preventing the access of unwanted users to any private information. The file lsass.exe also handles the password modifications done by the user.
The process lsass.exe mainly operates in the system through its ability to create access tokens. These tokens encapsulate the file’s security descriptor, which contains the necessary information to process user authentication such as data on which user holds access to the system and whether the access is mandatory or discretionary.
Note: lsass.exe is a process which is registered as a trojan. This Trojan allows attackers to access your computer from remote locations, stealing passwords, Internet banking and personal data. This process is a security risk and should be removed from your system.
Note: lsass.exe is registered as a downloader. This process usually comes bundled with a virus or spyware and its main role is to do nothing other than download other viruses/spyware to your computer. This process is a security risk and should be removed from your system.
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Since you can't seem to delete it the first thing to try is hold down shift then press delete while the file is selected, this removes it without putting it in the recycle bin, alternatively you can download AVG or Zonealarm, these are free virus programs and work well.
Zonealarm Download:
http://www.download.com/ZoneAlarm-Firewall-Windows-2000-XP-/3000-10435_4-10039884.html
AVG Download:
http://free.avg.com/download-avg-anti-virus-free-edition