Conficker is a computer worm that was first discovered in November 2008. It spreads through vulnerabilities in the Windows operating system and can infect computers without user intervention. Once a system is infected, Conficker can create a network of compromised machines, known as a botnet, which can be used for various malicious activities. The worm is notable for its ability to update itself and evade detection by security software. It has caused significant concern among cybersecurity experts due to its rapid spread and the challenges it poses in terms of removal and prevention.