Spam levels crept up again in July, accounting for 91.52 per cent of all email, according to messages scanned by SoftScan.

Despite the recently highlighted change in tactics by spammers to use PDF and Excel files to hide their messages, SoftScan attributes the rise to the fact that there is less legitimate business email around during July because many people are on holiday.

"Around this time of year we always see an increase in spam. However, further investigation of the data shows that it has not increased in real terms, but that legitimate email has decreased," said Diego d'Ambra, CTO of SoftScan.

"But spammers changing tactics around this time of year is bad news for businesses that don't have adequate protection. Spam that was once stopped before it reached those users' inbox is now getting through, leaving the holidaymaker returning to not just a full work load, but an inbox full of junk mail too."

Virus levels dropped again during July, from 0.61 per cent to 0.39 per cent of all email scanned. Phishing style viruses are also down from last month. However, since many viruses are distributed in waves of attacks, this lower figure is probably due to a dip in activity, not that the overall tactic of phishing has decreased, SoftScan said.