Conficker

 

First discovered in 2008, Conficker, which had many aliases, including Downup, Downadup, and Kido, is a worm that targets Windows operating systems. It uses a variety of different malware techniques, including exploiting flaws in Windows and using dictionary attacks on administrator passwords to infect computers and propagate, forming a botnet. It infected millions of computers in 190 countries, including those on networks run by the French Navy, the UK Ministry of Defence, and the UK House of Commons. Among the symptoms of Conficker are user accounts being locked, local area networks being flooded with traffic, and websites that host antivirus software becoming inaccessible.

Conficker was so troublesome that an industry group spearheaded by Microsoft and including ICANN and Verisign was formed to try and combat it.