Suspected Chinese government-backed hackers have breached computer systems of U.S. law firm Williams & Connolly, which has represented some of America's most powerful politicians, as part of a larger spying campaign against multiple law firms, according to a letter the firm sent clients and a source familiar with the hack. The cyber intrusions have hit the email accounts of select attorneys at these law firms, as Beijing continues a broader effort to gather intelligence to support its multi-front competition with the U.S.