Spam filters ability to accurately label and block junk mail is dropping, according to a report from security testing firm Virus Bulletin.
The company said in its VBSpam report that a test of some 21 different anti-spam platforms returned lower overall detection and only one product, SpamTitan scored high enough to earn VBSpam+ certification.
The results are part of a larger trend within the security space towards lower catch rates. The company said that overall catch rates have been trending downwards since March.
"We hoped this would be a one-off thing - perhaps the consequence of a new spam campaign," said Martijn Grooten, anti-spam test director for Virus Bulletin.
"But rather than bounce back, spam catch rates have continued to decline throughout the year."
Researchers and law enforcement have taken measures to cut spam rates as of late. Earlier this month, the shutdown of the Grum botnet lead to a temporary drop in spam rates of almost 20 per cent.
That drop, as with previous shutdowns, is expected to be only temporary and rates are expected to rise as new botnets are created and deployed for spam runs.
While effectiveness may be declining, Grooten noted that many of the products the company tested were still highly effective at catching spam attempts in most cases.
"It is important to realise we are still a very long way away from the scenario of email accounts becoming unusable because of the vast amount of spam," he said.
"We certainly haven't lost the war against spammers, but they have won an important battle."
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