The confirmed count of fraudulently-issued SSL (secure socket layer) certificates now stands at 531, said Gervase Markham, a Mozilla developer who is part of the team that has been working to modify Firefox to blocks all sites signed with the purloined certificates.

Among the affected domains, said Markham, are those for the CIA, MI6, Mossad, Microsoft, Yahoo, Skype, Facebook, Twitter and Microsoft's Windows Update service.

"Now that someone (presumably from Iran) has obtained a legit HTTPS cert for CIA.gov, I wonder if the US gov will pay attention to this mess," Christopher Soghoian, a Washington D.C.-based researcher noted for his work on online privacy, said in a Saturday.

Soghoian was referring to assumptions by many experts that Iranian hackers, perhaps supported by that country's government, were behind the attack. Google has pointed fingers at Iran, saying that attacks using an ill-gotten certificate for google.com had .

All the certificates were issued by DigiNotar, a Dutch issuing firm that last week admitted its network had been .