If you look at the announce URL in your torrent client you will see a long string of 'random' characters as part of the URL. That is called a passkey and each is unique per account. You can reset your passkey on most trackers, some do require staff to do it for you.

The trackers require a passkey, without one the tracker will not allow you to connect (therefore you can not download). With several IPs using the same passkey the account will typically be auto-banned or whatever the site setup their tracker to do