Third-party INF contains no information about signatures ?

When does this message arrive, on bootup, when going online, or what? What AV or anti-malware programs are running? You need to determine what is producing that message somehow in order to proceed. As signatures are mentioned it might be your virus checker, or some anti-malware program. If all else fails (and it happens on bootup) you press the "Windows key and R" then type msconfig in the Run box and temporarily disable any suspects you see in the Startup tab. Always pop back and let us know the outcome - thanks

This message appears at the beginning of driver installation. AV or anti-malware programs are absent.

What particular driver are you trying to install, sound, graphics or whatever? Do you know you can get perfectly reasonable free AV's, such as Avast, Microsoft Security Essentials and AVG? Always pop back and let us know the outcome - thanks

I'm installing USB driver with: [Version] Signature="$Windows NT$"

Did you get this driver from the computer manufacturers? Always pop back and let us know the outcome - thanks