Under the terms of the Vienna Convention, the only sanction available to a host country that suspects a foreign diplomat has abused his or her privileges is a declaration of the diplomat as persona non grata with a requirement to leave within a specified period. Expulsions may be ordered on an individual basis or occasionally in larger groups, an example being Operation FOOT in 1971 following the defection of Oleg Lyalin, a KGB officer based in London who revealed the extent of the intelligence professionals operating under diplomatic cover.