The amount of spam relating to gambling increased by 1,500 per cent in July, according to email security company Clearswift.

The company's monthly spam report showed that gambling was the growth area in July, possibly spurred by the World Poker Series and the flotation of gambling companies on the world's stock exchanges.

There also seems to have been something of a silly season last month. Various adverts offing superhuman powers, magic coins that can change your life or medicines capable of performing miracles have all appeared in inboxes worldwide.

"Spammers really appear to be taking the concept of the 'silly season' all too literally," said Alyn Hockey, Clearswift's director of research.

"Despite the fact that the claims are laughable, PC users should not click on these emails or forward them as jokes to colleagues.

"Not only is this software likely to be highly ineffectual, but by clicking on these emails you might infect your PC with spyware or pass your bank details on to a potentially insecure site."

Healthcare spam is still the most common form of junk email, accounting for 41 per cent of all spam. Financial products came in second at 31 per cent.