Spam accounted for 96.63 per cent of all email scanned in March, making it the third consecutive month that junk mail levels have remained steady.

However, security experts at SoftScan noticed a sudden 40-45 per cent drop in the amount of spam stopped at the first level of protection, the reputation filter, in the last few days of March.

"Although there was a significant drop in spam levels at the reputation filter, we did not see any drop at our main spam filters," said Diego d'Ambra, chief technology officer at SoftScan.

"This leads us to believe that spammers are cleaning up their infrastructure and are possibly starting to stop sending spam that will be automatically picked up by reputation filters.

"In some respects the drop in spam is good news, but it will not be long before the spammers reveal their next tactic to replace the 'missing' junk mail. "

SoftScan reported that virus levels remained typically low during the month at just 0.07 per cent of all email scanned.