If an anonymous text message includes a phone number, the recipient can perform an online search to find the source of the message. Some unlisted phone numbers can be unveiled by checking social networks or websites. If the text message was sent using a service, instant messenger or email, it is very difficult to trace.
When an anonymous text uses a real phone number, it can be traced even if the user does not recognize the number. Online searches can reveal numbers that were placed in directories. The search looks for the phone number as if it were a keyword, revealing every page where the number appears. Phone carriers can trace the text as if it were a phone call to reveal its source. Reverse phone look-up services can also be used for a fee.
Apps can be used to mask a phone number completely. When using these apps, users are able to send and receive messages without revealing their actual phone numbers. This makes the numbers impossible to trace. Similar services are also available through websites. Because the user never puts his phone number into the website, he is untraceable.
Unwanted anonymous messages can be blocked by the user. If the messages are threatening or harassing the user, the user can contact law enforcement and his service provider.