Marine Corps sources are stating emphatically that, contrary to some published reports from dubious sources, the Marines in Cairo were most definitely armed:

The Ambassador did not impose restrictions on weapons or weapons status on the Marine Corps Embassy Security Group (MCESG) detachment.  The MCESG Marines in Cairo were allowed to have live ammunition in their weapons.  The Ambassador and Regional Security Officer have been completely and appropriately engaged with the security situation. Reports of Marines not being able to have their weapons loaded per direction from the Ambassador are not accurate.

Some people will lie about anything if they think it will get them a headline.