Deep inside the computer worm that some specialists suspect is aimed at slowing Iran's race for a nuclear weapon lies what could be a fleeting reference to the Book of Esther, the Old Testament tale in which the Jews pre-empt a Persian plot to destroy them. That use of the word Myrtus" - which can be read as an allusion to Esther - to name a file inside the code is one of several murky clues that have emerged as computer experts try to trace the origin and purpose of the rogue Stuxnet program, which seeks out a specific kind of command module for industrial equipment. Not surprisingly, the Israelis are not saying whether Stuxnet has any connection to the secretive cyberwar unit it has built inside Israel's intelligence service. Nor is the Obama administration, which while talking about cyberdefenses has also rapidly ramped up a broad covert program, inherited from the Bush administration, to undermine Iran's nuclear program. The difficulty experts have had in figuring out the origin of Stuxnet points to both the appeal and the danger of computer attacks in a new age of cyberwar. For intelligence agencies they are an almost irresistible weapon, free of fingerprints. Israel has poured huge resources into Unit 8200, its secretive cyberwar operation, and the United States has built its capacity inside the National Security Agency and inside the military, which just opened a Cyber Command.