A loophole in the random number generator of Windows 2000 can expose users' email, password and credit card details, university researchers claim.

"This is not a theoretical discovery. Anyone who exploits this security loophole can definitely access this information on other computers," said Dr. Benny Pinkas from the Department of Computer Science at the University of Haifa.

Pinkas said all correspondence that emanated from a computer using Windows 2000 is susceptible to tracking.

According to the researchers, which also included university graduate students, this loophole enables hackers to access information that was sent from the computer prior to the security breach and even information that is no longer stored on the computer.

The researchers describe the Windows random number generator as a program that is "a critical building block for file and email encryption, and for the SSL encryption protocol" which is used by all Internet browsers.

"For example: in correspondence with a bank or any other website that requires typing in a password, or a credit card number, the random number generator creates a random encryption key, which is used to encrypt the communication so that only the relevant website can read the correspondence."

By finding out how this generator works, the researchers are able to compute previous and future encryption keys used by the computer, and eavesdrop on private communication."

"There is no doubt that hacking into a computer using our method requires advanced planning. On the other hand, simpler security breaches also require planning, and I believe that there is room for concern at large companies, or for people who manage sensitive information using their computers, who should understand that the privacy of their data is at risk," said Dr. Pinkas.

Microsoft's director of security response, Mark Miller, said: "Microsoft is aware of public reports of a vulnerability in Windows, specifically, regarding an encryption vulnerability in CryptGenRandom(). Our investigation has shown that this is a local information disclosure vulnerability and has no possibility of code execution and cannot be accessed remotely. The attack requires physical access to the system as well as the attacker having to be logged on to the computer. Microsoft's investigation is complete on all supported Windows systems and will take appropriate action to help protect customers, which may include providing a security update through the next service pack of Microsoft Windows, depending on customers' needs. Microsoft is not aware of customer impact at this time."

Although only Windows 2000 was tested, Dr Pinkas said that because both Windows XP and Vista used a similar random number generator, there is a chance they might be vulnerable too.