Sentence:  [I]dentities in the online world can be easily <WSD>spoofed</WSD>. Your ten-year-old daughter will know that a middle-aged man is not her age or gender when she sees him in the physical world. But as we have seen, that middle-aged man can easily pass himself off as another ten-year-old girl in the online world. 
Meaning of the word marked with <WSD> tags:  To falsify.