U.S. and European officials say Iranian scientists have neutralized the malicious computer virus “Stuxnet” that had paralyzed the operation of Iranian nuclear machinery.

The officials say the malware made its way into equipment controlling Iranian uranium enrichment centrifuges as early as 2009 and dealt a significant blow to operations.

However, it remains unconfirmed exactly when the computer virus was purged from the system.

Computer security experts say it remains unknown how the malicious code got into the Iranian nuclear equipment. But they raise the possibility that Israel created the malicious code with the support of the U.S.