A security firm claims to have prevented a major phishing attack from reaching its customers on Monday night.

SoftScan, a provider of hosted spam and virus filtering services, said that it stopped over 70,000 phishing emails purporting to come from the MidAmerica Bank from reaching its customers.

The messages threaten to deactivate the recipients' bank accounts unless appropriate action is taken.

SoftScan said that, while phishing emails normally account for around 40 per cent of all malware stopped by the company, malware only constitutes a small amount of the total email scanned by SoftScan, the larger proportion of which is stopped as spam.

SoftScan's statistics for June show that email containing malware represented only 0.36 per cent of all email scanned.

But with a tenfold increase in phishing emails on Monday night, this figure is now up at almost one per cent. This latest attack means that phishing emails now account for nearly 80 per cent of all malware stopped.

Bo Engelbrechtsen, corporate communications manager at SoftScan, said: " Phishing emails are always bad news and not just for those users lured into giving away confidential details.

"Although most people know not to respond to them, they still clog up bandwidth and cost organisations money in the long run.

"This one is no exception. The sheer volume alone will affect many companies' email communications if they do not have protection in place."