Activision has brought back the servers for classic games like Modern Warfare 2, Modern Warfare 3, and Call of Duty Black Ops 1 and 2 due to player demand. However, the servers were taken offline again because of a self-spreading worm virus. Concerns about the virus were raised by players, and Activision is investigating the issue. Hackers used hacked lobbies to target Modern Warfare 2 players and spread the virus. Researchers believe the hackers exploited bugs to execute malicious code on players' computers. Activision has previously experienced cybersecurity attacks, including an SMS phishing attack.