Windows 2000 users have been warned that a loophole in the operating system's random number generator can expose their email, password and credit card details.
"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.
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.