An average of 5,424 new malware-hosting websites were detected by security firm MessageLabs every day in October - an increase of 48.2% on September.
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The monthly increase was helped by the period leading up to Halloween, said MessageLabs. The firm said spammers were using Google's Blogspot blogging site to spread a large chunk of spam.
Fellow security firm Fortinet earlier this month said Google's Google Reader and photo site Picasa were being used to spread Trojans among Facebook users.
During October, MessageLabs said the global ratio of spam in email traffic from new and previously unknown bad sources was 69.7% - one in 1.43 e-mails. This was a decrease, however, of 0.4% on the previous month.