Almost a third of UK organisations have unpatched critical vulnerabilities compromising their IT security, new research warned today.

However, the NTA Monitor 2007 Annual Security Report also revealed that the number of vulnerable firms has fallen compared to 2006, when some 61 per cent were open to attack.

The report analyses data gathered from vulnerability tests conducted by NTA on UK companies in a wide range of industry sectors, including charities, education, finance, government, IT, law and retail.

Although the number of tests exposing vulnerabilities that may enable external users to gain unauthorised system access or disrupt service availability has almost halved, the picture is not bright for everyone.

While improvements in overall security have been achieved by most industry sectors, publishing and finance have seen an increase in the average number of vulnerabilities found per test.

For financial institutions, the average number of risks increased by 16 per cent year on year, while publishing saw an increase of 28 per cent.

Roy Hills, technical director at NTA Monitor, said: "There are a variety of ways of causing denial-of-service attacks, one of which occurs when a server is bombarded with more information than it can handle, resulting in legitimate users being unable to access or use the network.

"Other security flaws that our testing discovered could permit hackers to gain entry to corporate networks and change user passwords or delete files, which could wreak corporate havoc."

Of the 10 most commonly occurring critical vulnerabilities, seven were found in last year's report, indicating that these same issues continue to take their toll.

All of the top 10 high risk flaws are associated with services being made available to internet users, demonstrating that with increased functionality comes the threat of reduced security.

NTA Monitor recommends that companies: