It's only a matter of time before we see this here.
In February 2010, a Virginia man named Anthony Joseph Tracy was arrested because of his close links to Al-Shabaab. By then, he had smuggled over 270 Somalis into the country through Mexico. The identities and locations of very few were known.
The Mexican government has also confirmed that al-Shabaab is taking advantage of the border. Its police have arrested and released members of al-Shabaab on their way to the U.S. before.
Another Somali jihadist group doing this same thing is Al-Ittihad Al-Islami. A Somali in San Antonio, Texas was arrested in March 2008 on immigration charges. From June 2006 to March 2008, he earned at least $3,000 for every single person he snuck across the border, making up to $75,000 in a single day.
He confirmed that he knew exactly what he was doing when he brought Al-Ittihad Al-Islami members into the U.S. His sentencing memo said “he believed they would fight against the U.S. if the jihad moved from overseas locations to the U.S. mainland.”
Can't grab a link via my iPad for some reason, but the source is Clarionproject.org "Al-Shabaab's State Sponsors Make Attacks Like Nairobi Possible".