The warning: terrorists can attack anywhere.
Planes, buses, subways, trains and everywhere people gather in groups will see increased security in the week leading up to Sept. 11.
Federal and local law enforcement are adding eyes and ears to look for clues of any possible terrorist. The main concerns are individuals; they're called lone wolves who keep a low profile.
"The notion of trying to prevent attacks by radicalized Americans or people in this country lawfully is almost impossible," said former Sept. 11 Commissioner James Thompson.
"There are no credible threats of any kind basically because of the 10th anniversary of Sept. 11," said Steve Whitmore from the L.A. County Sheriff's Department.
But the sheriff's department isn't taking any chances. And neither is any other law enforcement agency locally or nationally because the possibilities are too high.
The FBI has been told to review all active cases and reach out to informants. The TSA will have a record number of patrols and armed so-called viper teams.
Arab terrorist leaders know the significance of Sept. 11 and the anniversary. And still fresh is the foiled underwear bomb plot targeting an airliner bound for Detroit on Christmas Day 2009, as well as the attempt to blow up U.S. parcel planes with explosives hidden in printers last fall.
"We just always err on the side of caution," said Whitmore. "We add more deputies, some in plain clothes, some you'll see. We are going to have more canines, more random baggage searches."
Report anything suspicious to the L.A. County Sherriff's Department at 888-950-SAFE.