The Mediterranean hosts about 30 percent of the world's merchant shipping operations, and since September 11, 2001, OAE warships have stopped, boarded and searched over a hundred suspicious vessels. The United States gathers most of the intelligence on suspicious ships, some of it from other nations. By getting more nations involved, more intel is brought into the operation. It's impossible to prove a negative, but there has been no seaborne terrorist attacks, and a number of the board and search operations have resulted in arrests and the seizure of terrorist gear.
Russian and American warships are cooperating to hunt down terrorist ships in the Mediterranean. This is all part of Operation Active Endeavor (OAE), which is a multi-national operation that searched for, and boarded ships suspected of involvement in terrorist activities. This operation was started shortly after the Sept. 11, 2001 attacks. OAE is actually a number of regional arrangements, with U.S. warships being present in all of them. The American fleet, which contains about half the naval combat power on the planet, is the only fleet that operates everywhere.