Atak was first discovered Monday. Although antivirus companies do not expect it to cause much damage, they say it will be a nuisance because it can generate a large amount of spam.
Graham Cluley, senior technology consultant for antivirus company Sophos, said authors of malicious software generally try to make the job of antivirus researchers as difficult as possible by adding confusing code and using evasion techniques.
"Atak tries to tell when someone is stepping through the code to analyze whether it is a virus or not. Often, a virus will contain lots of code that is designed to make it more complicated for (antivirus) companies to write the detections," Cluley said.
Mikko Hypponen, director of antivirus research at Finnish company F-Secure, said that although it is common practice for virus writers to protect their malware, this worm is exceptional.
"It is standard for worms to have layers of encryption--or armoring--to keep out snoopers, but this goes way beyond that. It tries actively to detect if it is being analyzed by antivirus research tools. If it thinks it is being analyzed, it stops running and shuts down," Hypponen said.
Atak is not thought to be a serious threat. But because of recent detection and in-built protection, the worm's full functionality has not yet been fully analyzed. However, it is known that the worm contains text that seems to threaten other well-known worms and viruses, such as MyDoom, Bagle and Netsky.
Hypponen said there is a possibility that Atak will try to seek out and destroy "rival" worms.
"We haven't been able to figure out if Atak tries to disable some of these viruses," he said. "The message implies it does contain some code that attacks other viruses."
Munir Kotadia of ZDNet UK reported from London.