Nasdaq Stock Exchange
Nasdaq. Reuters

The Nasdaq OMX Group’s (NDAQ) Internet site was penetrated by hackers Tuesday, posters said in an online forum that is used to discuss stocks. The breach did not affect any trading or commerce platforms, said spokesman Joe Christinat.

Nasdaq sent a message to users Tuesday informing them that their user names, email addresses and passwords may have been compromised.

“We have identified the issue and we are in the process of upgrading and restoring the community. We will notify you as soon as the community is live,” said the email, signed by Bruce Hashim, vice president of online services.

Users were advised to reset their passwords for the Nasdaq and any other site where they use the same password.

The site was down on Tuesday afternoon. “We are currently upgrading the NASDAQ.COM Community Site,” a message on the Web page read. “We apologize for the inconvenience.”

Nasdaq lists and oversees trading for many of the largest U.S. technology stocks such as Apple (NYSE:AAPL, Microsoft (NYSE:MSFT) and Google (NYSE:GOOG).

It has become common for hackers to break into low-value targets to take passwords and log-in details. This contributes to lists that are compiled into software that speeds up the process of hacking into secure sites that contain more valuable information.

This is the second time in two years that the Nasdaq has been hacked. In 2011 the exchange discovered suspicious files on its servers and called in the FBI.