Spam accounted for almost 90 per cent of all emails received by businesses in August.

Up to 87.49 per cent of messages received by companies were harmful or unwanted, according to a study by Panda Security.

The majority of infected messages carried email worms – a form of malicious code that copies itself across servers – or Downloader Trojans, which transfer malware onto a user's computer.

'Junk mail has become a damaging plague for companies who suffer very serious effects of lost productivity, and an unnecessary drain on networked resources', said Luis Corrons, Technical Director of Panda Labs.