The main reasons are, but limited to, tracking links a lead shared with others.
In that context visits to the webpage will be counted correctly. People who clicked the shared link will be counted as one (the original lead) rather than each one counted as an unique visitor.
Reviwing the activity log of those three leads may display a large number of repeated visits. The IP address is likely to be distinct for most activity records. The browser identification has a narrower variation but still displays nuances such as the original lead using Safari on Mac OS X and other entries displaying IE9 on Windows 64 bit.
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