The threatening Storm botnet has collapsed to just 5% of its original size, while web-based malware has increased by 23.3%, according to the April intellligence report of security software firm MessageLabs.
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The introduction of malicious software removal tools, which target and remove Storm infections, is deemed responsible for the sudden reduction in Storm-infected machines from an estimated two million to around 100,000, said MessageLabs.
The decline in the size of the Storm botnet is evident from the 57% decrease in malware-laden e-mails it distributed during April.
While the Storm botnet shrank, analysis of web-based malware showed that 36.1% of attacks were new in April, an increase of 23.3% since March.
MessageLabs identified an average of 1,214 new websites a day harbouring malware and other potentially unwanted programs, such as spyware and adware, an increase of 619 a day compared with the previous month, March.
"April was a month of unpredictability, with the mighty Storm botnet losing all but 5% of its anonymous army, and web-based malware reaching new levels," said Mark Sunner, chief security analyst at MessageLabs.