Openfire defines "groups", to organize users into a single entity for easier management. These groups can be 'shared', meaning that the users in the groups are added as roster items to the users that the group is shared with.

org.jivesoftware.openfire.group.AbstractGroupProvider defines the method getSharedGroupNames(org.xmpp.packet.JID) that, based on the a provided JID, returns the names of all groups that are shared with that JID.

This method appears to return the names of all groups, not just the ones that are shared with the provided JID.

In certain scenario's, this can have severe consequences, as the processing of a shared groups can be resource intensive.