US online brokerage firm Scottrade said Friday it was notifying some 4.6 million customers about a hack into its database which could have leaked private information.

Scottrade said in a statement it was notified of the incident by US federal officials who "recently informed us that they've been investigating cybersecurity crimes involving the theft of information from Scottrade and other financial services companies."

The company said it believes that "the illegal activity involving our network occurred between late 2013 and early 2014, and targeted client names and street addresses."

"Although Social Security numbers, email addresses and other sensitive data were contained in the system accessed, it appears that contact information was the focus of the incident," the statement said.

"We have no reason to believe that Scottrade's trading platforms or any client funds were compromised. Client passwords remained fully encrypted at all times and we have not seen any indication of fraudulent activity as a result of this incident."

Scottrade said it was working with "a leading computer security firm" to assess the impact of the breach and strengthen its network.

It said it was notifying customers of the hack "as a precaution."

The news comes one day after T-Mobile said 15 million customer records may be been leaked in an attack on credit monitoring bureau Experian, and follows a series of other high-profile incidents involving corporate and government databases.