One of the biggest attacks in recent years was Conficker, a computer worm targeting Microsoft Windows systems, first detected in November 2008. It used software flaws and dictionary attacks on administrator passwords to propagate and was very difficult to counter because of its combined use of many advanced malware techniques.

Conficker  infected an estimated seven million government, business and home computers in over 200 countries, making it the largest known computer worm infection since the 2003 SQL Slammer. The diagram below outlines its operation:

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