Technet has a very good article around why such an attack is brutal and how to protect against it
Microsoft feels this could even lead to attackers pushing malware via Windows automatic update
Impact of this hack:
Update 07-Sep-11:
Not surprisingly, the same hacker which attacked Comodo, has taken the responsibility of this hack
To make matters worse, he claims to have compromised four other Certificate Authorities (CA)..!!
Update 09-Sep-11:
Fox-IT has published a very good report on the incident
ComodoHacker claims he can now exploit Windows Update as well
Update 12-Sep-11:
Update 27-Sep-11:
DigiNotar has filled for bankruptcy, plus the Dutch government has revoked their root cert
Dutch govt tells us how difficult & time consuming it is to replace all digital certs in an organization.
Update 01-Nov-12:
Fox IT now details the attack
Update 01-Nov-12:
Fox IT now details the attack