The L.A. Times has a report on millions of illegal aliens poised to enter the U.S. due to talk of amnesty. They obtained internal border patrol documents that, among others, have this to say:

"Possible terrorist cell groups may exploit this high influx phenomenon," one agent wrote. "[O]ur immigration system may in fact become over burdened to the point that many individuals may fall through the cracks allowing subjects that may be affiliated with terrorist groups to enter the country without being identified, or stopped."

See also the earlier AP report 'Illegal Entry From Mexico to U.S. Spikes'.