This number is a telemarketer for a trade magazine called Secure Computing. I have received dozens of calls from them. If you don't answer, they never leave a message. Of the half dozen times that I have answered, I finally got a response from someone. Usually, the line would just go dead.
It doesn't matter they won't take you off. These are crooks calling you to steal money. If they break the law, why would you think they would honor your wishes?