Pornographic spam tripled during May from 5.62 to 14.05 percent of all spam, according to an internet security firm.
Clearswift's Monthly Spam Index categorised spam emails and examined trends over the course of the month.
As well as the rise in the amount of pornographic related spam, the Spam Index also highlighted the re-emergence of e-cards bearing malicious software.
The company said e-card spam lured recipients into installing malware and was traditionally popular around Christmas.
Peter Croft, managing director of Clearswift Asia Pacific, said that email threats came in all guises and organisations needed to be prepared.
“Anti-virus is a good start but it’s nowhere near enough," Croft said in a statement. "Companies need to use intelligent content filtering software which can block executable files for the most robust defence possible.”
Clearswift said the highest profile spam during May was a message claiming pop star Michael Jackson had committed suicide. The message carried a weblink which installed a trojan on the recipient's computer.
The strangest spam reported by Clearswift took advantage of the buzz around the launch of the reality TV show Big Brother in many European countries. The emails invited contestants to eat a spoonful of maggots on live TV.