So the other day a friend of mine called me with an issue. It started when "HP support" called his wife saying that her network was infected. They proceed to gain remote access to her computer and started to do who knows what. At this point her husband came home and she excitedly told him that HP is fixing her computer. He immediately became suspicious and accidentally hung up. However, the helper still had access and proceeded to change the password of her windows account preventing her from being able to login.
Quickly and wisely he powered off the computer, and gave me a call before any further damage could be done. So the moral of the story is that HP, Microsoft, Yahoo, Samsung or any other company is not going to give you a call personally to help you out. Think about it, you probably couldn't even get help from them if you tried and called them. If one of these scammers calls just tell them you'll have your IT guy a call to check it out and hang up. If you are worried that you actually might have a problem give me a call and I'll see about putting your mind at ease.
On a similar note be aware of any pop ups while you are surfing the web saying your computer is infected, they are just as unlikely to be real and are a scam to sell you some fake software as another friend of mine found out. He called me in a panic one day, which after I arrived to evaluate the situation I discovered that he was running Linux which that has a low chance of viruses.
Jason