Hi, my name is ***** ***** I'll be happy to help you with this!
These messages are NOT legitimate. This is a scam that is going around right now where you will encounter a message saying that your computer has been hacked or you have a virus or something along those lines and that they will resolve the problem for you for a fee. The whole thing just a ploy to get money from you.
The way it works is that small tech companies will pay third-party advertisers to insert their phone numbers into these pop up messages. So what you're actually seeing is a carefully crafted advertisement. If you called the number you'd talk to someone (probably with a foreign accent) who will ask to connect to your computer and then will try to sell you on some kind of support services you don't actually need.
Sometimes these companies will claim to be Microsoft or HP or some other well known company. This is always a lie.
If you receive these messages in the future, simply close them out. If it won't let you close it out, then you can hold down the power button on your computer for 5 to 10 seconds to do a hard shutdown. Once you restart your computer the message should be gone.
If you have any other questions on this, just let me know and I'll be happy to answer them for you.
NOTE: If you have no further questions, please use the rating box at the top of the page to rate the answer at least 3 STARS/OK SERVICE or better to end our session for now. I will standby until the answer has been rated.