He realized that the same theory used to block spam could also be used to kill HIV.

And some Internet service providers block spam to subscribers.

Both commercial firms and volunteers run subscriber services dedicated to blocking or filtering spam.

I have a filter that purports to block spam.

Even greater are the costs of trying to block spam, catch spammers and undo the damage they cause.

So far, nothing that has been tried to block spam has done much more than inconvenience mass e-mailers.

Nonetheless, their list is widely used by Internet service providers looking to block spam.

His reCaptcha project (recaptcha.net) seeks to block spam while handling the challenge of digitally scanning old books and making them available in Web search engines.

We want it to block spam and viruses, even when Macs are clients.

The company also released several free tools for its members to block spam, viruses, and spyware.