Report: Spam filters are getting worse

Industry stalwart Virus Bulletin releases sobering report about state of commercial spam filters. Bottom line: We may be in for another round of problems

Virus Bulletin, probably best known for its VB100 antivirus test award, also periodically tests commercial spam filters. Its March 2012 report is out (summary; PDF report for subscribers), and the news isn't good.

Most commercial spam filters caught significantly less spam this time around than in other recent tests. The false positive rate's up, too.

VB put 20 commercial spam filters through the wringer. They're measured against real-time bombardment, over the course of 16 days, of more than 200,000 emails -- 190,000 of which were spam. The testers measured the spam catch rate, typically more than 99 percent. They then deducted five times the false positive rate to come up with a final score. Final scores ranged from a low of 98.62 percent, to a high of 99.97 percent.

All of the tested products "passed" and were awarded VBSpam certification. The top product, Libra Esva, received a new award called VB Spam +.

But the clean slate of winners masked several lurking problems.

IP address blacklisting isn't working as well as it used to: "We didn't just see a few dips in spam filters' performance: for all but one product the catch rates were lower than in the previous test... products had a significantly harder time blocking messages based on the IP address from which they were sent. This may be because DNS blacklists have become less accurate than they used to be, or because spammers have been sending more spam using legitimate mail servers."

Also, the overall spam catch -- which usually stays above 99.5 percent -- fell well below 99 percent twice, both due to German language spam, first for rogue pharmaceutical companies, then for phishing emails looking for credit card details.

With several of the biggest botnets now on the skids, the volume of spam seems to be falling. But if spam filters are losing their effectiveness -- particularly if spammers are coming up with effective new ways to circumvent the filters -- we may be in for yet another round of problems, based on a lower volume of more intelligent spam.

How did your spam filter fare? VB has a graph that shows the bottom-line results.

This story, "Report: Spam filters are getting worse," was originally published at Get the first word on what the important tech news really means with the InfoWorld Tech Watch blog. For the latest developments in business technology news, follow on Twitter.