Throughout the 1950s and 1960s, the U.S. Federal Bureau of Investigation (FBI) and police departments kept lists of known homosexuals, their favored establishments, and friends; the U.S. Post Office kept track of addresses where material pertaining to homosexuality was mailed. State and local governments followed suit: bars catering to gay men and lesbians were shut down, and their customers were arrested and exposed in newspapers. Cities performed "sweeps" to rid neighborhoods, parks, bars, and beaches of gay people. They outlawed the wearing of opposite gender clothes, and universities expelled instructors suspected of being homosexual.