Thursday the FBI circulated a counter-terrorism warning to law enforcement that said Al-Qaeda may be planning attacks on shopping malls in Chicago and Los Angeles during the holiday season. It now says the warning was not backed by specific intelligence.

The law enforcement sensitive information was leaked by ABC news on its Website.

FBI officials told the Chicago Tribune and the Los Angeles Times that similar warnings have been circulated each holiday season for several years.

"This document was intended for law enforcement and intelligence community partners for situational awareness," the FBI said in a statement. "In the post-9/11 era, sharing information is our top priority. Al-Qaeda messaging has clearly stated they intend to attack the U.S. or its interests; however, there is no information to state this is a credible threat. We remind people to remain vigilant and report suspicious activity to authorities."

PoliceMag.com reminds all readers that shopping malls are a prime target for terrorism. They are open to the public, full of potential victims, and an attack on a mall, especially during the holidays, would damage the U.S. economy.

The Rand Corp. has outlined a series of measures that it says could greatly reduce the risk of attacks at enclosed shopping centers, including public information campaigns alerting people to report suspicious packages, placement of vehicle barriers at pedestrian entrances, and clearly identified exits so shoppers can leave malls quickly in an emergency.

"In the past these sort of [law enforcement warnings] have caused a lot of anxiety and consternation for shopping mall operators because they haven't been sure about how to respond," Tom LaTourrette, lead researcher on the Rand project, told the Los Angeles Times.