Talking to him by phone, with software filters, had been bearable.

And software filters pose the same risk of inadvertently blocking desirable e-mail messages, especially since spammers have found ways to make their messages look ordinary.

In 2000, Congress passed a law requiring schools and libraries receiving certain kinds of federal money to use software filters.

To that end, software filters, which were first developed to search for objectionable words and block access to sites containing them, now often work from a list of approved sites.

But Mr. Shimomura is now at work on a software filter that he hopes will make it easier to ward off such attacks.

In fact, the current software filter contains about 85% political keywords, and only 15% pornography-related keywords.

It skips objectionable scenes based on software filters created by human editors and stored in its memory.

A type of software filter that would let parents and other individual users screen access to material they might find offensive is supposed to become available on Compuserve within a month.

Some of those software filters are already available from companies including Surfwatch Software Inc., Los Altos, Calif.