U.S. authorities are investigating whether a hacker is behind the online publication of a cache of Morgan Stanley's client data and not the financial adviser who was fired in connection with the breach, the Wall Street Journal reported, citing people familiar with the matter.

Morgan Stanley last month fired financial adviser Galen Marsh for allegedly stealing account information from about 350,000 of its wealth management clients and posting some of it online.

Federal law-enforcement officials are focusing their probe on the possibility that Marsh's computer was hacked, the Journal said.

It is unclear who might have been responsible for the hack and officials haven't arrested anyone in connection with their ongoing investigation, the newspaper said.

Morgan Stanley said that the leaked information included clients' names and account numbers, but not passwords or Social Security numbers.

The company said at that time it was investigating the breach and has referred the matter to regulators and law enforcement authorities who are conducting separate investigations. The FBI and FINRA were among the enforcement agencies looking into the matter.

Representatives of Morgan Stanley, FINRA and the FBI were not immediately available for comment outside regular U.S. business hours.

The leadership team of Morgan Stanley's wealth management business has been visiting brokerage offices around the country to reassure advisers and clients in the wake of the data theft.