The free version can only be used in a private environment - for example if you help friends or relatives in your free-time and do not receive any money for it. Commercial use is every usage which has to do with your work life. This means that if you use it at work or support customers and colleagues it is commercial usage. Therefore you are not allowed to use the free version of TeamViewer in any office environments. As soon as one of the PCs participating in a session is connected to a commercial network (office/school/etc.) it is considered commercial use.
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