Conficker (also known as Downup, Downadup Kido) is a computer virus/worm that was coined on Microsoft Windows machines in October 2008. The virus used a leak that had previously been closed, but many consumers and businesses did not always have the latest version of security updates, so it could quickly spread.
Conficker largely spreads through networks. If the worm finds a vulnerable computer, it shuts down the automatic backup service, removes existing restore points, shuts down certain security services, blocks access to a number of security Web sites, and opens ¯ Nfecteerde Computers to set up even more programs from the worm maker. The worm then tries to spread itself to other computers on the same network.
How can you remove Conficker, read it here.