Same thing happened to me. I called the number they picked up straight away and were asking for personal information. I didn't give them any information I just told them it was a work computer and then they started asking me about my home computer [Why? The virus was on the work computer?] so yeah I ended the conversation there.. pretty sure it's something dodgy.

This is a number that came up in a pop-up message when I was on the internet, advising to ring for help after being on the internet. My computer was overtake by the message stating "This is a Mac System warning". The message kept on repeating and was coming up in one of those pop-up ads that give you a countdown and option to skip, but didn't skip. I didn't call the help number, as I wasn't sure if it is a scam.