4. Conficker: $9.1 billion
Conficker was discovered initially in 2008 and it exploited network service vulnerability on Windows 2000, XP, Vista, Server 2003, Server 2008 and Server 2008 R2 Beta. A more dangerous variant appeared in the end of 2008 and it added the ability to spread over the local network. Conficker was notorious for its ability to attack military organizations. Some French Navy’s aircraft were unable to fly, some Royal Navy warships were infected and Germany armed forces, Bundeswehr, also reported limited infection in its network.