SoftScan is predicting a 40 per cent surge in junk email during September as spammers target students returning after the summer break.

The security firm has already seen a "dramatic rise" in the past few days as spammers perfect their techniques with e-card and document spam.

A range of new types of spam have started to circulate in recent months as spammers try to find ways to circumvent filters.

Many spammers now embed messages into various document formats including PDFs, Word files and Excel files.

There has also been a significant rise in e-card spam, where users receive an email containing a link to an e-card purporting to come from a friend or family member.

"It is a pattern we have seen in previous years, but this September looks as if it will be the largest increase yet," said Diego d'Ambra, chief technology officer at SoftScan.

"Although we cannot predict with absolute certainty that this tendency for an increase in spam in September will continue, there are some strong indications.

"Spammers are constantly improving their methods to get past the filters. Last autumn it was image spam, but this year they have switched their attention to document and e-card spam."

Hackers often target students returning after the summer break, many of whom will unwittingly bring in laptops already infected with malware which will spread when they connect to communal networks.

"Students' surfing habits makes them the perfect target for malware writers, " warned d'Ambra.

"Careless users who surf the net, spend time in chatrooms and play online games without sufficient protection on their laptops will inevitably become infected, normally without their knowledge.

"These machines are probably already part of a botnet before they are brought into campuses, providing an easy backdoor to the vast resources of any institution not properly protected."