Spam levels rose by five per cent last month to reach over 90 percent of all email, according to the latest figures from cloud-based security vendor MessageLabs.
The firm's monthly Intelligence Report found that spammers are increasingly sending unsolicited emails from webmail accounts hosted by legitimate providers.
The rise has been driven in part by an increase in messages containing a subject line and link to social network profile pages created by automated Captcha-breaking tools, the report said.
"As spam levels continue to increase, we are seeing existing attack techniques combine and morph into one," said Paul Wood, senior analyst at MessageLabs.
"In 2008 Captcha-breaking, social networking spam and the use of webmail for spamming all became popular tactics.
"Today, the bad guys are using the three together as a triple threat to heighten the effectiveness of their spamming."
The report also found that users in Europe tend to receive a steady stream of spam throughout the day, while those in the US witness a peak between 9am and 10am.
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