The Sans Institute has some controversial advice for computer security professionals looking to lock down their networks: spear-phish your employees.

That's what the US Military Academy at West Point did in 2004 to a group of 512 cadets, selected at random for a test called the Carronade. The cadets were sent a bogus email that looked like it came from a fictional colonel named Robert Melvillle, who claimed to be with the academy's Office of the Commandant (the real Robert Melville helped invent a short-range naval cannon called the carronade nearly 250 years ago).

"There was a problem with your last grade report," Melville wrote, before telling the cadets to click on a web page and "follow the instructions to make sure your information is correct".

More than 80 percent of the cadets clicked on the link, according to a report on the experiment (click here to read a PDF of the report).

Worse still, even after hours of computer security instruction, 90 percent of freshmen cadets still clicked on the link.

Spear-phishing attacks contain this kind of targeted information in order to seem more credible, but their goal is the same as a regular phish: trick the user into doing something they shouldn't, such as giving up sensitive information.

Because these attacks rely on co-operation from their victims, it's hard to prevent them, said Alan Paller, director of research at Sans. "The only defence against spear-phishing is to run experiments on your employees and embarrass them," he said.

Paller's organisation compiles an annual report on the top internet security targets. This year 'human vulnerabilities' will make their first appearance on a list that is typically made up of software products such as Internet Explorer, databases and filesharing applications.

That's because the human factor is being exploited in a growing number of targeted attacks as more and more online criminals come online in Eastern Europe and Asia, Paller said.

Although Microsoft Corp.'s Windows operating system has long the prime target of online attackers, the software giant has tightened up its security practices over the past few years.

But that hasn't deterred attackers, Paller said. In fact 2006 witnessed a surge in attacks that take advantage of unpatched vulnerabilities in new types of programs, such as office applications, media players, backup software and VoIP (voice over IP) servers, Paller said.

"We've been pretending that the problem would go away as Microsoft got better, but we forgot that every other company wrote software with as little care for its security as Microsoft did," he said.

Changes to the Windows OS (operating system) have prevented widespread worm attacks from spreading, but internet users are no more secure than they were during the time of Sasser and Slammer, Paller said.

"The average user is significantly less secure," he said. "And it isn't because the vendors have got worse at all; it's because the number of bad guys has exploded."

The 2006 Top 20 Internet Security Vulnerabilities report will be unveiled today in conjunction with the National Infrastructure Security Co-ordination Centre.