Industrial spies or sophisticated computer intruders may cause a diversion to gain access to a building or secure area. One diversion used is to release a harmless chemical known as butyl mercaptan into the air. The effect is to create the impression that there is a natural gas leak. Once personnel start evacuation procedures, the bold attacker uses this diversion to either steal information or to gain access to enterprise computer systems. Another tactic used by information thieves involves remaining behind, sometimes in a restroom or closet, at the time of a scheduled evacuation drill, or after setting off a smoke flare or other device to cause an emergency evacuation.