It sacked the worker responsible and called law enforcement authorities.
Shares in the bank fell further than those in the rest of the sector on the announcement, as regulators are increasingly keen to make sure financial institutions are properly looking after client data.
As many as 10 per cent of its wealth management clients have been affected, but the bank maintains nobody has lost money from the data breach.
The account names and numbers of around 900 clients were briefly posted online, with partial data from a total of 10 per cent of the unit’s clients leaked. It is thought that the bank discovered the leak in a regular online security sweep.
“The wealth management employee has been terminated, and law enforcement and regulatory authorities have been advised of the incident,” said the bank in a statement. “The firm is taking the precaution of notifying all potentially affected clients and instituting enhanced security procedures including fraud monitoring on these accounts.”
A senior industry figure said that Wall Street banks are doing all they can to protect data, but if an insider is determined, then a risk always exists.
“If the will exists to behave badly, there is always a chance. It is like a house – you can have all the security you want, but if someone really wants to break down your door, they will be able to do it,” the banker said.
Morgan Stanley’s shares slid 3.13 per cent on the day.