The U.S. may be vulnerable to cyberattacks. Some experts advocate both new international agreements aimed at preventing cyberwar and world cooperation to trace back attacks. "We're really at the beginning of the conversation," says Duncan Hollis of Temple's Beasley School of Law, a former State Department attorney working on treaty negotiations. It's "not a legal black hole — no one's saying there are no rules — but how do these existing rules apply in this context?" The rules of war depend in large part on knowing who attacked you, Hollis says, and that can be hard to figure out when it comes to cyberattacks.