Tom Cruise has reportedly stepped up security at the L.A. home he shares with wife Katie Holmes and daughter Suri, after his production offices were targeted by an anthrax hoaxer.

Last month, a series of anthrax threats were sent to Los Angeles' MGM Tower, which houses the actor's film studio, United Artists.

The premises were evacuated on both occasions, before the LAPD determined them to be a hoax.

But Tom – who fears he was the target of the threats – is taking no chances and is said to have boosted security surrounding himself and his family.

"Tom fears the threats were directed at him," a source tells the Mail on Sunday.

"He has tightened security in the office and the Scientology church in Hollywood and installed state-of-the-art cameras at his mansion in Beverly Hills. It's like Fort Knox."

Tom has adopted children Connor, 13, and Isabella, 15, with ex Nicole Kidman, 41, and Suri, 2, with Katie.