Storm Worm is a trojan horse attack baiting people with weather information. It spreads through emails. The email carries the subject "230 dead as storm batters Europe".
People who open the attachment becomes part of a botnet, which attackers can exploit later without the knowledge of the user. It's kinda social engineering in that it tries to fool people by giving timely alert about current deadly weather conditions prevailing in most parts of the world. The attachment is an executable file which promises to give more details about the weather conditions. Opening the attachement creates a backdoor which can be later exploited later to steal data or use post malicious spams.