The amount of spam has trebled since June and now makes up 90 per cent of all email traffic, according to a US report.

The massive increase in spam messages is due to criminal gangs using so-called botnets to send out spam, US email security company Postini said.

During this year's Christmas shopping period the amount will rise even further, the report showed. In June, 2.5 billion spam emails were sent across the world, increasing to seven billion in November.

The spam emails are primarily sent from the US, China and Poland, according to security company Marshal . Spamhaus , the project aiming to track spammers, estimates that some 200 criminals gangs are behind 80 per cent of all spam emails. Anna Lagerkvist