Spam now accounts for 79 per cent of all emai, according to figures from email security firm BlackSpider Technologies.

This represents a 10 per cent rise from the start of the year.  

Quocirca security analyst Jon Collins says the increasing proportion of spam to genuine email is not surprising.

'Spam is almost expanding in tandem with Moore's law. It will continue to increase as the resources for pumping it out go on growing. Until effective legislation is introduced to stop it at source, we can expect spam on the internet to continue increasing in an almost exponential way,' he said.

Forrester analyst Paul Stamp says that while spam being sent is continuing to increase, it is likely that the amounts reaching inboxes will continue to reduce as filtering technologies and authentication systems become more efficient.

'The nature of the threat from spam is chaging. Instead of just selling Viagra, we are now seeing spam now combine with things like phishing and spyware,' he said.

'It is going to be ever more important for companies to have anti-spam gateways in place, but also to be able to augment those with web-based content solutions to stop people surfing malicious sites.'