Can hackers delete mobile phone messages?

This behavior of hackers is illegal. If the user realizes it, he can call the police.

Article 40 of the Constitution stipulates that the freedom and privacy of communication of the people and citizens of China shall be protected by law. When public security organs and procuratorial organs check communication according to the procedures prescribed by law, no organization or individual may infringe upon citizens' freedom and privacy of communication for any reason, except for the needs of national security or criminal investigation.

Article 252 of the Criminal Law stipulates that whoever conceals, destroys or illegally opens other people's letters and infringes upon citizens' right to freedom of correspondence, if the circumstances are serious, shall be sentenced to fixed-term imprisonment of not more than one year or criminal detention.