In one example, a first group of users is selected among a plurality of possible groups based on a score generated for the first group, the score indicating appropriateness of the first group for the first user, the first group of users having a plurality of users. A first user is then added to the first group of users. Then, affinity levels between the first user and other users in the first group of users are measured, the affinity levels indicating how strong logical relationships are between the first user and the other users in the first group of users. The first user is then removed from the first group of users in response to a determination that the affinity level between the first user and the other users in the first group of users has dropped below a preset threshold over time.