Why are security vendors faking digital certificates?

Kaspersky Lab got in touch at the end of last week to say the number of untrusted digital certificates used to sign off malicious software had doubled in the last year, with its anti-virus database highlighting more than 6,000 of the things, just to put this into context. A little context is never a bad thing, as there are plenty of sysadmins who routinely trust digital signatures without any further investigation and are happy to install signed files on this flawed trust assumption, which is worrying.