Microsoft has added its voice to the chorus from rival browser makers, notably Google and Mozilla, about the seriousness of the situation. Like its competitors, Microsoft will also permanently block all DigiNotar certificates.

"We are in the process of moving all DigiNotar owned or managed [certificate authorities] to the Untrusted Root Store, which will deny access to any website using DigiNotar certificates," said Dave Forstrom, a director in the Microsoft Trustworthy Computing group, in an emailed statement Sunday.

Forstrom did not set a date by when Microsoft would block all DigiNotar certificates, including those used by the Dutch government, which has been a major customer of the company.

Google updated Chrome on Saturday to block all DigiNotar certificates, while Mozilla plans to do the same on Tuesday for Firefox.

However, Microsoft's partial ban of DigiNotar certificates -- which it instituted last week -- and the complete sanction now in the works only protects users running Windows Vista, Windows 7, Windows Server 2008 and Windows Server 2008 R2.