A new program that disguises computer attacks so that they can skip past network barricades has raised the stakes in the arms race between hackers and network administrators. The latest version of the program Fragroute can be used to beat at least one popular security fortification, or Intrusion Detection System (IDS). Computer security researcher Gunter Ollman, of Internet Security Systems in the UK, says the new program uses various well-known techniques to test a computer’s defences. But the program also applies a new trick to defeat IDS programs, he says. “It is interesting. But it is really down to a lack or foresight on the part of IDS designers, Ollman told New Scientist. “It’s a constant arms race.” Data are usually split into small chunks for easy transportation across the internet and IDS programs vet these packets to prevent malicious commands from hackers getting through. Fragroute exploits a discrepancy between the method by which computer operating systems and some IDS programs put the packets back together. Some packets are repeated when sending data and certain IDS programs, including a popular free one called Snort, only use the packets sent first to reconstruct the whole. In contrast, most operating systems use the later duplicate packet. This means the IDS can inadvertently allow through packets disguised as duplicates that have a damaging effect when put back together by the target operating system. Ollman says the new technique does not affect most commercial IDS programs. Other experts have said that repairing affected IDS programs should not be difficult or time-consuming. Fragroute was created by security researcher Dug Song, of US company Arbor Networks, to highlight the potential weakness and test network defences.