Forgery and interception happened all the time. So did just pure confusion and chaos. Here is a lovely example from the legendary Battle of Karánsebes:
Immediately, the hussars and infantry engaged in combat with one another. During the conflict, some Romanian infantry began shouting, "Turcii! Turcii!" ("Turks! Turks!"). The hussars fled the scene, thinking that the Ottoman army's attack was imminent. Most of the infantry also ran away; the army comprised Austrians, Romanians, Serbs from the military frontier, Croats, and Italians from Lombardy, as well as other minorities, many of whom could not understand one another. While it is not clear which one of these groups did so, they gave the false warning without telling the others, who promptly fled. The situation was made worse when officers, in an attempt to restore order, shouted, "Halt! Halt!" which was misheard by soldiers with no knowledge of German as "Allah! Allah!".[5][6]