In addition to the IP address, most people put lots of information about themselves on the internet.
For instance, if you used the same username in that chat room as here then someone could tie you to this Yahoo account and know that anything mentioned here is also about you. Purely based on the questions you have asked on here I would guess that you are between 25 and 40, you live in the UK and you are a football fan.
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Digital Marketing Agency|SEO UK