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Tom Cruise

Theo Wargo/WireImage.com

What has more potential explosions than a Tom Cruise movie? A Tom Cruise office building, it turns out.

For the second time this week, Los Angeles' MGM Tower, a professional complex that houses the production companies of both Cruise and Salma Hayek, has been hit with a security threat, this time over an anthrax scare.

Sources confirmed exclusively to E! News that a building-wide memo has gone out informing all tenants of anonymous threat phoned in to the building's main switchboard stating that deadly virus would be placed into the building's ventilation system, starting on the 20th floor.

The Cruise-run studio United Artists is housed on the tower's 11th floor; Hayek's Ventanarosa production company is located on the second.

It's not immediately clear whether either star was at the office building today.

A memo circulated earlier today claimed that "due to lack of credibility of the threat, the building, LAPD and MGM are not recommending that we take any actions." Despite the assurances, Los Angeles police have since been called to the Century City site.

An updated notice confirmed that the building's management dispatched engineers to examine the ventilation system and no signs of tampering have been found.

Nonetheless, the management is still taking precautions, blocking outside air from entering the building and tightening security on the complex's heat- and air-control rooms by prohibiting tenants or guests from entering the areas. Any contractors on site today are being escorted around the premises by security.

Additionally, several companies located within the MGM complex have issued a list of symptoms indicative of anthrax poisoning.

It's the second big scare this week.

On Tuesday, the tower was evacuated for roughly four hours after an anonymous bomb threat was called in to one of the building's tenants (though not to the companies of Cruise or Hayek).

The LAPD was called to the scene and determined that it was a hoax.