IBM's Global Security Index for May has reported a 226 per cent increase in phishing attacks over the previous month.

The surge in attacks was attributed to the rise of zombie botnets, networks of hijacked computers used to pump out huge volumes of scam emails.

Viruses and worms, such as Sober.N and Mytob, also continued to spread rapidly through email and web applications. Around 30 per cent of emails monitored contained some form of virus, a rise of 33 per cent.

Application hacking is now the predominant form of attack on targeted systems. Applications are considered just as vulnerable, but are not as high on IT managers' agendas for patching.

Spam email showed no growth, accounting for 68 per cent of all inbound email monitored by IBM.

Meanwhile, in its monthly report for June, email security specialist Postini recorded the second highest level of phishing attempts since it began tracking. Only March was higher.

The company claims to have protected its customers from 16.5 million phishing attempts, 71 per cent up on the previous month.

Postini also noted a reduction in virus attacks as well as attempts to cull company directories, known as directory harvest attacks.