The latest monthly report from security firm MessageLabs lists spam loads at 85 per cent, an increase of more than 9 per cent from last month.
Much of the rise was attributed to a sharp jump in the use of image spam, which uses a .GIF or .JPG file rather than plain text.
The tactic emerged in late 2006 as a way to defeat anti-spam filters but was thought to have fallen out of favour. Now, MessageLabs believes that spammers are again using the technique to bypass protections.
"These images are now being hosted on what appear to be trustworthy hosting sites, whilst taking advantage of redirection links from reputable sites in order to obfuscate the true location of the image hosting," the company said in the report.
"This is also a technique employed by spammers to evade spam filters that examine the domains of hyperlinks contained in the email."
The latest spike follows a larger trend of rising spam levels over 2009. Worldwide spam levels plummeted in the fall of 2008 following the shutdown of hosting firm McColo, but have more than recovered this year as spammers have migrated to new providers.
Most recently, spammers took advantage of panic surrounding the Swine Flu outbreak to flood mailboxes with links to online pharmacies.