Posted by Virus Bulletin on Jun 17, 2013
Most filters see a small increase in their catch rates overall.
The results of VB's latest spam filter test show that the spam sent from web hosts is significantly harder to block than spam sent via other means.
Following various reports on the amount of spam sent from compromised web hosts, we compared delivery rates for spam sent from web hosts with that of other spam - and found that the former kind of spam was more than three times as likely to make it past a spam filter.
This is a big difference, even if delivery rates remain low: spam sent from web hosts had a 1.04% chance of making it past a spam filter, compared to 0.29% for other kinds of spam. As a single spam campaign easily sends millions of emails, this difference can make or break the campaign.
In recent years, the security community has placed a lot of focus on botnets of compromised home PCs. Recently, however, cybercriminals have turned their attention to web hosts, many of which are easy to compromise and have good and reliable Internet connectivity. The results of this test show that this isn't merely a quantitative shift, but that by sending spam from web hosts, spammers can signficantly increase their delivery rates.
Most of the 20 full solutions tested saw an overall improvement in their spam catch rates since the last test - although catch rates didn't fully recover to their previous levels.
There was good news for most of the products in the test: 19 full solutions reached the required standard to achieve a VBSpam award, and two of them - Bitdefender and Libra Esva - combined a very high catch rate (99.50% or more) with a lack of false positives and thus earned a VBSpam+ award.