What a month. Human frailty, spam and a dangerous Microsoft Windows vulnerability combined to produce four major Internet worm attacks in August. A rundown:\n\n\n\n The W32.Mimail, a mass e-mailed worm, looks like a system administrator\u2019s message.\n\n The W32.Blaster Internet worm exploits a flaw in Windows\u2019 implementation of the remote procedure call (RPC) protocol and spreads worldwide in a matter of hours, infecting hundreds of thousands of Windows machines. \n\n Others emerge that exploit the same vulnerability as Blaster, including W32.Welchia, which disrupts networks while PC users try to patch the RPC vulnerability.\n\n A new version of the Sobig worm, W32.Sobig.F, bombards e-mail accounts worldwide. \n\nExperts agree that these worms are so effective because they spread rapidly via e-mail, they attack Windows, and they are relatively easy to assemble. The only consensus about prevention is on how much work it takes: for Microsoft, antivirus vendors and user companies. \n\nCIO John Halamka of CareGroup and Beth Israel Deaconess Medical Center says a combination of firewall, network intrusion detection systems, antivirus software and patches worked to keep his facilities worm-free during the outbreak. Halamka\u2019s IT staff held what he called an "all nightmare-athon" patching session in late July for the hospital\u2019s 130 Windows servers. Worm-free, yes. Cost-free, no.