A method for determining group membership in a computer system, the method comprising: obtaining an identifier that describes a member of a group, the member of a group having a member hash table that contains group membership information describing to what groups a member belongs; performing a primary search of a plurality of groups to determine if each group contains the member's identifier, each group in the plurality having a group hash table that describes to what other groups the group belongs, caching the results of the primary search in the member hash table, for each group to which the member belongs, performing a secondary search of a plurality of groups to determine what groups contain the group to which the member belongs, and caching the results of the secondary search into the group hash table and merging the results into the member hash table, and reading the member hash table to determine group membership.