Every week seems to bring another story of email theft. The attacks are relentless, striking corporations, government agencies and political groups. Now they’re hitting law firms, too.

Fortune recently reported that a series of break-ins at top U.S. firms was much wider than originally thought and linked to the Chinese government. According to Fortune, the attackers stole tens of gigabytes of data from one firm alone, possibly amounting to hundreds of thousands of emails. The article adds, “The hackers returned repeatedly in search of new information.” No wonder. Law firms, with their troves of confidential client data, make tempting targets for criminals bent on insider trading, blackmail or industrial espionage.