Sea attack by "unconventional" means?

Washington Times op-ed piece on the topic of Attacks on the US -from the sea:

Ports oversee the annual movement of some 6 million containers, of which the U.S. Customs and Border Protection (CBP) Agency inspects perhaps 3-5 percent. Indeed, CBP has little counterterrorism intelligence to support its efforts.
In all, an estimated 7,500 foreign-flag vessels make some 51,000 U.S. port calls each year.
Yet, an attack from the sea may not necessarily come from a container offloaded from a ship.
Instead, merchant ships under terrorist control could be fashioned into floating nuclear bombs. It wouldn't take many such vessels and terrorists with state-sponsor support are assessed to have such a capability.
These terrorist ships, however, would not have to enter into a U.S. port. They only would need to come near one, thereby bypassing the much-ballyhooed "National Maritime Security Strategy" of container security.
It also would make useless Customs' Container Security Initiative program at selected foreign ports. That said, authorities still would need to expend the resources to insure against the use of containers to smuggle contraband or weapons of mass destruction.