...if you receive a message like this and don't recognise the number DO NOT RUN IT.
I suggest that even if you DO recognize it, don't open it.
People tend to trust services which they associate with people they trust, and they shouldn't.
The malware author wins the first round of the fight to get his malware onto your system by default when a user ascribes an inappropriate level of trust to something that is not actually their friend, but with which they associate their friend.
My Friend's Service Accounts (email, facebook account, phone number, etc) =/= My Friend.
I also suggest changing Windows folder view options to uncheck the box for "hide extensions for known file types."
The reason is that naming a file CuteKitten.jpg.exe doesn't change the fact that it is still an executable, but if you have that option checked what you will see is CuteKitten.jpg.
With this option checked, what you should see for a real JPG would just be CuteKitten because JPG is also a known file type, but in your mind what you might think you see is a JPG file because the .exe extension is hidden.
Hiding information from yourself in this way leaves you open to that split second between your finger automatically clicking the mouse button to see the picture and your brain saying "AArrgh! NO! that's not a picture"
This is in my opinion a HORRIBLE default file view option.