Yes, they would have the ability to compromise all PCs (ARM, x86). Notes, though: * All BIOS-based PCs and many ARM-based PCs (as well as other CPU-based unit

Yes, they would have the ability to compromise all PCs (ARM, x86). Notes, though: * All BIOS-based PCs and many ARM-based PCs (as well as other CPU-based units) are currently vulnerable. As others have noted, this is not a very active threat vector compared to, say, Flash bugs and infected software ("...to view this p0rn, you have to install this codec" - bam! you are pwned). * Ability to bypass the key signing via a stolen key is necessary but not sufficient for an attack. You also have to get (trick) the user into installed infected boot-type code. The advantage is that you can then install rootkit-class software, which is very very hard to detect and eradicate. * People with "powerful" keys take extensive measures to protect them. Having said that, people with "powerful" keys have slipped up, which causes a lot of problems. Examples: Microsoft's key (an old one) was hacked and used to sign the "Flame" virus, Mozilla's private key revealed, the RSA key token hack. References: http://news.cnet.com/8301-10805_3-57446466-75/flame-virus-spread-through-rogue-microsoft-security-certificates/ http://news.cnet.com/8301-10805_3-57446466-75/flame-virus-sp... http://www.itnews.com.au/News/252766,comodo-hacker-reveals-mozilla-private-key.aspx http://www.itnews.com.au/News/252766,comodo-hacker-reveals-m... http://blogs.computerworld.com/17995/rsa_securid_hacked_2fa_fob_and_software_compromise http://blogs.computerworld.com/17995/rsa_securid_hacked_2fa_...