Federals are trying to identify hackers, who have repeatedly entered the network of the company that runs the Nasdaq Stock Market during the past year, the Wall Street Journal reports.

Although the part of the network system that executes trades was not compromised, investigators are trying to decipher the possible motives behind the penetration. A range of motives are being considered from theft of trade secrets to unlawful financial gain and even threat to the national security.

So far, (the perpetrators) appear to have just been looking around, the Wall Street Journal quoted a person involved in the matter.

The probe was initially instigated by the US Secret Service but now, the Federal Bureau of Investigation is looking into the matter to identify the perpetrators and their motive.

Hacking of company websites have recently increased at an alarming rate with countries like the US, China, Russia and parts of Europe being affected the most.

The Associated Press reports that in 1999, a group of hackers calling itself United Loan Gunmen infiltrated the computer that runs the websites for Nasdaq and the American Stock Exchange.

The case is regarded as one of the largest hacking crimes in U.S. history, wherein the penetrators claimed to have briefly created for itself an e-mail account on Nasdaq's computer system.