As we and others have reported for years now, China is often accused of infiltrating the computer networks of U.S. companies and government departments. At the RSA security conference in San Francisco this week, one expert said that U.S. officials consider China just the most prolific on a shortlist of four countries most actively probing U.S. assets over the Internet.

Appearing on a panel about cyberwar, James Lewis, a fellow at the Center for Strategic and International Studies who previously served in the U.S. departments of State and Commerce, had this to say: