My mobile phone always receives some short messages about real estate information, and the numbers are all ordinary mobile phone numbers. How did they know my number? Depressed …

Information leakage may be that you were bought by others when you were applying for a job and delivering your personal information, or that postcards were sold by others. You can call 10086 to block those numbers. If you are a smart phone, you can download a 360 (only for mobile phones) and put it on the blacklist. Some mobile phones have blacklists themselves.