One of the most recent and disturbing trends we have seen is an increase in intruder compromise and use of routers

Computer Emergency Response Team

The first DoS attacks took place in February 2000 when popular sites such as Yahoo, Amazon, eBay and CNN were knocked offline by being bombarded with bogus data packets.

At the time, anyone wanting to carry out these attacks had to use largely manual methods to find and compromise machines that could launch data packets on their behalf.

The response to these high-profile attacks meant that the tactic used to generate the net traffic, known as smurfing, became much more difficult to carry out.

But as one loophole closed, attackers moved on to develop new methods and strategies. Now tools are available that can automatically scan for vulnerable machines and infect them.

Once infected, machines can be made to report their readiness to net chat services. Many attackers co-ordinate the machines under their control via the same chat channels.

Closing window

One new strategy is causing particular alarm. "One of the most recent and disturbing trends we have seen is an increase in intruder compromise and use of routers," said the report.

Routers are hardware devices that pass data packets around the net. They are attractive to attackers for very simple reasons.

"Routers are often less protected by security policy and monitoring technology than computer systems, enabling intruders to operate with less chance of being discovered," warn the authors.

The routers are being used to scan for vulnerable machines, to hide links to chat channels used to control compromised machines, as well as to launch streams of data packets.

The report paints a grim picture of the future and said DoS attacks were likely to prove "attractive and effective" in the future.

To make matters worse, security experts who protect sites from attack are getting less and less time to learn about new threats and ways to counter them.

The report said: "The window of opportunity between vulnerability discovery and widespread exploitation, when security fixes or workarounds can be applied to protect systems, is narrowing."