The company that runs the Nasdaq stock market says the hacking attempts were detected during a regular security scan and did not affect its trading systems.
The motive is unknown.
The targeted application is called Directors Desk.
It's designed to make it easier for companies to share documents with directors between board meetings.
It also allows online discussions and Web conferencing within a board.
A spokesman for Nasdaq OMX says the Justice Department asked his company to keep silent about the hacking attempts until at least Feb. 14.
However, The Wall Street Journal reported the investigation yesterday.
Nasdaq is the largest electronic securities trading market in the U.S. Directors Desk carries strategic information for about 300 companies.
