For many traditional domain migrations, the use of sIDHistory is a common vehicle to avoid disruptions. As users and groups are migrated to other domains, they inherit new SIDs. This is because SIDs are domain specific. So historically problems arose when users and groups attempted to access resources in the source domain. Because the DACLs (Discretionary Access Control List) of the source resources are still attuned to the original SID's, users who migrated to a new domain or forest would be denied access. So to circumvent this starting with Windows 2000 Microsoft introduced the sIDHistory attribute. The premise of this attribute is to store the users or groups SID from the previous source domain and append it to the access token along with their new SID. Now users and groups in the midst of a migration could have access to source resources like file servers that have yet to be migrated.