Trucks carrying freight over the border must describe their cargo in advance in electronic messages to customs officials beginning in November, the Homeland Security Department (search) said Tuesday.

The electronic manifest (search) must be received at least 30 minutes before the truck attempts to enter the United States. The information will be compared with law enforcement and commercial databases to target potentially dangerous shipments that need to be inspected. Mislabeled cargo or a shipper's record of past violations might cause cargo to be labeled high risk.

The new security rules were supposed to take effect in March, but they were delayed because the government's computer software had to be adapted.

Truck companies now have three separate deadlines -- November 15, December 15 and January 14 -- depending on where they enter the country.

Congress ordered the changes last year because of fears that terrorists could smuggle chemical, biological, or nuclear weapons into the country.

Only a tiny percentage of air, rail and truck cargo is currently inspected.