The American Library Association (ALA) reports that recent acts of vandalism can help libraries identify the targets of future vandalism.[20][21] The ALA has recommended additional security measures or relocation of library materials relating to past vandalism.[20] The University of Memphis Library had problems with common reference books missing pages or indexes and therefore chose to move these items behind information desks and implementing a gatekeeper system for use.[22] However, restricting access to books is considered by the library profession as a "limitation of access to information which poses a threat to knowledge pursuit and exchange."[23]