The providers are upfront about what their services are used for.

Here's how one company, Tecom, its service: "Usually, your web hosting provider will shut down your web site within days, or even sooner, if they find out you are sending bulk e-mails and directing people to your site on their server. Bullet-Proof Web Hosting helps you to direct customers to your web site, and you won't have to worry about being shut down because of spam complaints."

Tecom says its services, which are hosted in "major cities in China," cannot be used for online gambling or pornographic material, however. China's Ministry of Public Security has cracked down on Internet pornographers since the mid-1990s.

When a domain is being used for spam or to spread malicious software, security researchers usually use an established protocol to report the domain to its registrar, who can then remove it from the Internet.

That doesn't work with bulletproof domains, because the registrars simply ignore the take-down requests. "I think there's some confusion about how the Internet community needs to work together," Warner said. "There are just these grey spaces [for Chinese companies] ... 'Should I have to terminate a domain because an American company told me to?'"