Why do you sometimes need a mobile phone verification code and sometimes you don't?

In order to prevent some people from using automatic login software to obtain other people's passwords.

Computer login qq music sometimes requires mobile phone verification code, and sometimes it is not necessary to prevent some people from using automatic login software to obtain other people's passwords.

There is "login protection" in the settings of mobile QQ. Only when this option is turned on, mobile phone authentication is required when logging in on a new device, especially when logging in on a new computer. If this function is not turned on, you don't need to turn on QQ for security authentication.