In Windows NT, 2000, and XP, what is the SID (security identifier)?

Question

In Windows NT, 2000, and XP, what is the SID (security identifier)?

Answer 1

A security identifier (SID) is a unique value of variable length that is used to identify a security principal or security group in Windows operating systems. Well-known SIDs are a group of SIDs that identify generic users or generic groups. Their values remain constant across all operating systems.

Here is a list of SIDs used in Windows Operating Systems

http://support.microsoft.com/kb/243330