So it appears that a build server at Adobe was compromised, and the criminals managed to make off with a code-signing certificate bearing a shiny “Adobe Systems Inc.” string.
The code signing certificate has already been utilized to sign malware. Adobe say they will shortly revoke the certificate and have it added to Verisign’s certificate revocation list.
Full details at http://blogs.adobe.com/asset/2012/09/inappropriate-use-of-adobe-code-signing-certificate.html
Please note that the certificate was NOT stolen. Adobe has stringent security measures in place to protect its code signing infrastructure. The private keys associated with the Adobe code signing certificates were stored in Hardware Security Modules (HSMs) kept in physically secure facilities. We confirmed that the private key associated with the Adobe code signing certificate was not extracted from the Hardware Security Module (HSM). For details, please refer to the blog post referenced above.