The security breach at the Dutch Certification Authority DigiNotar proved to be much more serious that previously estimated.

Hackers used the stolen SSL certificates to sign forged certificates for the domains of spy agencies such as the US Central Intelligence Agency (CIA), the British spy agency MI6, and the Israeli secret service Mossad.

DigiNotar, a subsidiary of VASCO Data Security International Inc., suffered a cyber attack in July, in which hackers produced hundreds of forged certificates for third-party domains.

With the help of forged certificates hackers can potentially access users' login credentials by spoofing a legal site, complete with a functioning but a forged SSL certificate.

The Dutch public broadcaster NOS published a list of fifty domains for which forged certificates were issued.

On Saturday, the Dutch government declared that it can't guarantee the security of its own websites in wake of the sophisticated hack.

Meanwhile, Dutch Interior Ministry spokesman Vincent Van Steen said they were investigating if Iran played a part in hacking its websites.