IT managers must be on their guard following a sharp rise in pornographic and healthcare-related spam, security firm Clearswift has warned.

According to the company, pornographic spam has leapt by almost 350 per cent since June, while there has also been a significant rise in healthcare spam.

Clearswift observed that spam content tends to change seasonally, with this summer's upsurge in pornographic junk mail following a similar rise last year.

Spammers now appear to be "purposefully" increasing their output of pornographic spam for the summer, Clearswift warned.

Alyn Hockey, Clearswift's research director said: "Companies can find their reputations compromised by the infiltration of pornographic email, especially when it's not managed effectively."

"In addition to the obvious offence these images can cause, a large percentage of these emails attempt to dupe users into opening viruses that are maliciously hidden within web links or zipped attachments."

Last week the National Hi-Tech Crime Unit warned of Trojan software hidden in a website which includes a keylogger to steal sensitive information, and a program that allows an infected PC to act as a mail proxy for spammers.