Spam levels in April fell 65 per cent year on year as cyber criminals continue to struggle with the Rustock botnet shutdown, although phishing has risen thanks to the continued prevalence of automated toolkits on the underground market, according to Symantec.
The security firm's latest monthly State of Spam report found average daily spam volumes down 5.35 per cent in April, continuing the trend seen in March which witnessed a drop of 27 per cent thanks to the Rustock shutdown.
Overall, spam made up 74.81 per cent of all messages in April, compared with 74.68 per cent in March. By comparison, the percentage of spam was 89.22 in April 2010.
Amada Grady, senior threat analyst at Symantec, explained that Rustock at one point accounted for over 47 per cent of all spam globally, although she warned that the cyber criminals are already looking to build new botnets.
"In April 2011 on some days as much as nine per cent of all spam globally contained an attachment and at least one per cent of all spam globally contained a known malware attachment - this is a significant increase from March," she added.
"While a profit motivation behind spam continues to exist it is likely that volumes will increase again but it's too early to speculate as to whether they will reach pre-Rustock levels."
The report also found that the "overall phishing landscape" increased by over 15 per cent in April, while phishing web sites created by automated toolkits grew by about 26.19 per cent.
As always, scammers have been using popular events or news hooks to dupe victims. Mother's Day in the US and the death of Osama bin Laden were two typical examples in April.
Web users are once again warned not to click on suspicious links, to ensure that their operating system is up to date with the latest patches, and to be selective about web sites at which they register their email address.
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