While we sleep, they get busy.
False flag (or black flag) describes covert military or paramilitary operations designed to deceive in such a way that the operations appear as though they are being carried out by other entities, groups or nations than those who actually planned and executed them. Operations carried during peace-time by civilian organizations, as well as covert government agencies, may by extension be called false flag operations if they seek to hide the real organisation behind an operation.
The name "false flag" has its origins in naval warfare where the use of a flag other than the belligerent's true battle flag as a ruse de guerre, before engaging an enemy, has long been acceptable. Such operations are also acceptable in certain circumstances in land warfare, to deceive enemies in similar ways providing that the deception is not perfidious and all such deceptions are discarded before opening fire upon the enemy.