The initial period of idealism for IMARO ended, however, with the Vinitsa Affair and the discovery by the Ottoman police of a secret depot of ammunition near the Bulgarian border in 1897. The wide-scale repressions against the activists of the Committee led to its transformation into a militant guerilla organization, which engaged into attacks against Ottoman officials and punitive actions against suspected traitors. The guerilla groups of IMARO, known as "chetas" (чети) later (after 1903) also waged a war against the pro-Serbian and pro-Greek armed groups during the Greek Struggle for Macedonia.