The Los Angeles' MGM Tower, a professional complex housing production companies, sent out a building-wide memo informing all tenants of the anonymous threat with the deadly virus.
The call had come in to the building's main switchboard, stating that the deadly virus would be placed into the building's ventilation system, starting on the 20th floor, sources confirmed exclusively to E! News.
It is not known if Cruise, who has his studio United Artists housed on the tower's 11th floor, and Hayek, whose Ventanarosa production company is located on the 2nd, were present at the time.
The threat was not taken seriously and a memo was circulated on August 9 claiming, "due to lack of credibility of the threat, the building, LAPD and MGM are not recommending that we take any actions."
But despite the assurances, Los Angeles police have since been called to the Century City site.
To prevent any mishaps, the building's management had dispatched engineers to examine the ventilation system and no signs of tampering were found.
To further ensure that nothing can get in to the building the management blocked outside air from entering the building and tightened security on the complex's heat- and air-control rooms by prohibiting tenants or guests from entering the areas.
Further, any contractors on site are being escorted around the premises by security, and in addition to it, several companies located within the MGM complex have issued a list of symptoms indicative of anthrax poisoning.