How does OPPO phone intercept short messages?

Take OPPO R9S mobile phone as an example, the setting method is as follows:

First, open the "Settings" icon on the mobile phone desktop to enter.

Second, after entering the settings, select the "Information" option.

Third, then find the item "harassment interception" and click enter.

Four, after entering, turn on the "block new information notification of strange numbers" switch.