The prank is annoying for SETI@home users, and it's troublesome to commercial efforts to launch similar "distributed computing projects" which work by tapping into the personal computers of thousands or millions of participants via the Internet.

Two Stanford University graduate students recently announced their scheme to thwart users who have been submitting false results or claiming more SETI@home work than they really did to gain glory on the project's Web page. But that process is useless to protect against this sort of hack.

SETI@home users participate in the project by downloading and installing software to crunch space signals collected by a huge radio dish at the Arecibo Radio Observatory in Puerto Rico. When operational, the program appears as a vibrant purple signal-graph screensaver on computers. The processed data are returned to the project's servers in Berkeley with an ID number attached, and a computer there then sends another "work unit" back to the volunteer's e-mail address.

Hackers inserted themselves into that moment in the process and hijacked e-mail addresses by submitting a range of ID numbers to the servers, project director David Anderson told MSNBC.com.

Anderson estimates that hackers absconded with as many as 50,000 e-mail addresses and then sent e-mails that menaced users' privacy.

Once users started alerting SETI@home managers, they responded by no longer sending out e-mail addresses. No other personal information, including passwords and real names and addresses, was compromised, Anderson told MSNBC.com, but hackers could still get usage statistics about volunteers separate from e-mail addresses.

Eventually, SETI@home would like to set up clients with passwords, but the project currently lacks resources for that. For now, the project has funds to continue through the end of the year.