The Ministry of Defence went to extraordinary lengths to cover up its true involvement in investigating UFOs, according to secret documents revealed under the Freedom of Information Act. The files show that officials attempted to expunge information from documents released to the Public Records Office under the 30-year rule" that would have revealed the extent of the MoD's interest in UFO sightings. The ministry wanted to cover up the operation of a secret unit dedicated to UFO investigations within the Defence Intelligence Staff. The files were made public following FOI requests by David Clarke, a lecturer in journalism at Sheffield Hallam University and his colleague Andy Roberts. "These documents don't tell us anything about UFOs but they do show how desperate the MoD have been to conceal the interest which the intelligence services had in the subject," said Dr Clarke. A [1976] note from the UFO desk to the MoD's head of security [states] "It is undesirable that even a hint of this should become public and we are currently consulting...on ways of expurgating the official records against the time when they qualify for disclosure." In a note dated April 28 1993 from DI55 to the public UFO desk the unnamed author argued the unit's involvement should be excised from records due to be released under the 30-year rule.