A plan to bump up the bandwidth bills of spammers seems to be getting out of control.
The screensaver uses idle computers to tackle spam sites
Earlier this week Lycos Europe released a screensaver that bombards spam websites with data to try to increase the cost of running such sites.
But analysis shows that, in some cases, spam websites are being completely overwhelmed by the traffic being directed their way.
The Lycos plan has also come under fire for encouraging vigilantism.
Lycos Europe's "Make love not spam" campaign was intended as a way for users to fight back against the avalanche of junk mail messages coming their way.
Participants were encouraged to download the Lycos screensaver which, when their PC was idle, would then send lots of data traffic to websites that peddle the goods and services mentioned in spam messages.
Lycos said the idea was to get the spam sites running at 95% capacity and generate big bandwidth bills for the spammers behind the sites.
The screensaver has reportedly been downloaded more than 90,000 times since it was launched.
But monitoring firm Netcraft has analysed response times for three of the sites the screensaver targets and has found that the campaign is being too successful.
Two of the sites being bombarded by data have been completely knocked offline. One other site has been responding to requests only intermittently as it struggles to cope with the traffic the screensaver is pointing its way.
Some sites are being knocked out by the anti-spam campaign
The downing of the sites could dent Lycos claims that what it is doing does not amount to a distributed denial of service attack (DDoS). In such attacks thousands of computers bombard sites with data in an attempt to overwhelm them.
Finnish anti-virus firm F-Secure advised against using the screensaver in case of legal problems.
Currently laws in many countries do not explicitly outlaw DDoS attacks but many nations are re-drafting computer use laws to make them specific offences.
Lycos Europe has yet to comment on this latest development in its anti-spam campaign.
However, the company has denied reports that the "Make love not spam" website was hacked earlier this week.
Some users of the site claimed to have got back a message that said: "Yes, attacking spammers is wrong. You know this, you shouldn't be doing it. Your IP address and request have been logged and will be reported to your ISP for further action."
Lycos said the supposed defacement of the site was a hoax. It added that its campaign must be having an effect if spammers were adopting such tactics.
The law has yet to catch up with some aspects of net life
It said that the strong interest following reports on news sites such as Slashdot had made the anti-spam site slow to respond.
The campaign has come under fire from some corners of the web.
Many discussion groups have said that it set a dangerous precedent and could incite vigilantism.
"If you do manage to swamp the spammers then you set yourself up for more attacks in return," said Graham Cluley, senior technology consultant at anti-virus firm Sophos.
"Having this screensaver in a large company could slow down your internet connection," he said. "And what is to stop a mistake happening and the wrong number going on the list?"
Mr Cluley urged users not to respond to anything in spam messages.