Security researchers working to find more information about the RSA breach earlier, have discovered the email which led to the theft of sensitive data.

The phishing email, which was sent to four employees of RSA's parent company EMC, contained the letters, "I forward this file to you for review. Please open and view it." The email did not include any undersign and urged the employees to simply open the file.

The hackers were able to breach the security system of the company and steal undisclosed information relating to RSA's SecurID tokens that are used by 40 million employees around the world. Researchers are looking into the breach as the stolen information aided the subsequent hack of defense contractor Lockheed Martin and other firms using RSA systems.

"We knew that the attack was launched with a targeted email to EMC employees (EMC owns RSA), and that the email contained an attachment called 2011 Recruitment plan. xls," said Mikko Hypponen, the chief research officer of security firm F-Secure.