The mobile phone received a very evil message.

There should be two possibilities for this: first, there may be a problem with your local network, which led to this problem. This has nothing to do with it. It's normal. Don't worry. Second, it is possible that the person who texted your friend deliberately hid his mobile phone number. Now many mobile phones have the function of hiding numbers. If so, either someone is playing a prank on your friend or doing something bad to your friend. Analyze yourself, personally, I prefer the second possibility, because the possibility of the first case is too small and basically impossible, so let your friend find someone he doesn't know.