Trojan Horse virus is a destructive program that masquerades as a useful program. Trojans do not replicate themselves like viruses. Users install Trojans thinking them to be legitimate programs. However, Trojans can contain viruses that destroy or corrupt the data and programs on the network. Trojans can also corrupt software applications. Like the name suggests, a Trojan can bring other viruses and worms with itself. A Trojan can be concealed within any software. Trojans can also be created by using existing utility programs. Most modern anti-virus packages can detect Trojans. However, it is difficult to determine whether a new program is a Trojan or not.