Others didn't send me a message, and I automatically replied on QQ. Almost every day, someone asked me what was going on, which made me very depressed.

Check whether your qq number has been stolen first, and then check whether you have set up automatic reply operation on qq. If you still can't find out the reason in the end, please update the qq number, which will avoid many troublesome problems.

Supplementary answer:

This should be a normal reply from qq system (I thought it was a malicious message at first), because its form is similar to chatting with a computer. When you haven't replied to the netizen who sent the chat message for a period of time, the system will send a sentence indicating that you are busy; Or when your qq logs in, the system will send out phrases to help you find a chat partner.