Most viruses target computers with the Microsoft operating system. Virus authors use social engineering and exploit detailed knowledge of security vulnerabilities to gain access to their hosts' computing resources. New viruses are created using complex anti-detection/stealth strategies to evade antivirus software such as Bitdefender. There are many reasons/motives for creating viruses, such as seeking profit, wanting to send a political message, personal amusement, demonstrating the existence of a vulnerability in software, sabotage and denial of service, or simply because they want to explore, challenge and have fun. In 2003, an Internet worm called Slammer, also known as Sapphire, caused a denial of service attack on some Internet hosts and significantly slowed general Internet traffic. It caused $1,200,000,000 in damage and infected 200,000 computers. It is one of the top five viruses of all time.