We rely on public-key cryptography to authenticate software we download from the Internet, like software updates, some Web-based software, and many device drivers. When we try to install or run such software, the system may automatically check the signature and warn us if it is missing or suspect. The system checks the signature by referring to a public-key certificate associated with the vendor who signed the software.
So what happens if the public-key certificate is fraudulent?
For that matter, what makes a certificate fraudulent, and how would such a thing arise?
A certificate is fraudulent if the name it carries does not accurately reflect the person or entity that actually controls the associated public/private crypto keys. And yes, there have been several cases of fraudulent public-key certificates.