The East Coast isn't the only part of the country that's on high alert. Hollywood's now on guard after the FBI warned the area's movie studios Thursday about possible terrorist attacks, reports Variety. As a result, studio entrances were shut down, barricades were put in place and some studio tours were cancelled. "The FBI provided a threat advisory to the movie studios in Los Angeles," confirmed Cheryl Mimura, a spokeswoman for the FBI. "The uncorroborated threat states that a film studio in California could be the target of a terrorist attack in retaliation for any possible bombing attacks by the United States in Afghanistan. It seems to be a credible threat." The heightened security means that most studios will have only one entrance and there will be several security measures in place at those entrances. And although the studios will try to get on with movie- and TV-making, the heightened security alert has resulted in increased tension on the lots. At Paramount, executives went ahead with a screening of the new "Star Trek" TV series, but only after some debate. And Warner Bros. has closed three studio gates, set up barricades and installed armed guards and metal detectors. The studio is also X-raying all incoming packages and searching some vehicles.