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.
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.