Via the US Office of Naval Intelligence:

The following is a maritime warning for mariners operating in the Gulf of Oman, North Arabian Sea, Gulf of Aden, and the Bab el Mandeb regions. Be advised, elevated regional tensions have increased the risk of potential maritime attacks being conducted by extremists. Vessels at anchor, operating in restricted maneuvering environments, or at slow speeds should especially be at heightened states of awareness for any suspicious activity. Report the presence of any craft behaving in a suspicious manner towards vessels–to include loitering, photographing, and conducting unauthorized approaches–to the proper authorities.