5. Code Red – $2 Billion
Code Red appeared on July 2001 and attacked Microsoft IIS web server. It exploited an indexing bug and ironically, the maker of the virus used information described in a security bulletin issued by Microsoft a month before. Just like other destructive viruses, it also took advantage of a buffer overflow glitch. Code Red defaced affected websites and displayed “HELLO! Welcome to http://www.worm.com! Hacked By Chinese!”