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The circle of friends generally refers to a social function on Tencent WeChat, which was launched on April 20, 2002, when KLOC-0/9 updated WeChat version 4.0. Users can post words and pictures through friends circle, and share articles or music to friends circle through other software. Users can "comment" or "like" a friend's new photo, while other users can only view the comments or likes of the same friend. There is a hidden switch in the WeChat settings-the circle of friends is visible for three days. Usually, this hidden setting is rarely used because most people are lazy. More than 1 100 million people have established a circle of friends visible for three days. This switch is used most in WeChat. This function is a very effective self-defense mechanism.