You see them mentioned in the news all the time. DoS and DDoS attacks are on the rise, and they are getting more sophisticated and intense every year. The US government accused Iran of conducting a prolonged series of DDoS against the web sites of Bank of America and other financial institutions, presumably as retaliation for economic sanctions levied against Iran for its nuclear program. Recently DDoS attacks by extortionists have targeted banks in Greece and Sweden. So what are DoS and DDoS attacks?