Security experts are warning that terrorists may be using virtual worlds such as Second Life "to meet and exchange ideas".
So says the Intelligence Advanced Research Projects Activity (IARPA), a US intelligence body which looks at developing technologies.
"The virtual world is the next great frontier and in some respects is still very much a Wild West environment," the organisation states.
"Unfortunately, what started out as a benign environment where people would congregate to share information or explore fantasy worlds is now offering the opportunity for religious/political extremists to recruit, rehearse, transfer money and ultimately engage in information warfare or worse with impunity."
The agency has recommended setting up systems to monitor online activity. The CIA already has a virtual presence in Second Life.