Major US law firms including Cravath Swaine & Moore, and Weil Gotshal & Manges, and others suffered cyberattacks last year, but it is yet to be determined what information was breached or if it was for illegal insider trading purposes, a Wall Street Journal report says.

The Manhattan U.S. attorney’s office and FBI last year began an investigation into the attacks. Officials from Weil Gotshal have not yet commented on the incident, while Cravath said in a statement that the incident did not have a major impact on its systems. Weil Gotshal and Cravath both represent Wall Street banks and Fortune 500 companies in merger negiations and lawsuits, for instance.

Security firm Flashpoint had issued alerts and notices to law firms in past few months to warn about possible outbreaks, as had the FBI. 

Read more about the cyberattack campaign against law firms in the Wall Street Journal report.