BT is very popular and some trackers do not allow non-member to leech from them to guarantee share ratio of the whole system. Below are interesting promotions for closed tracker.
- Bonus credit - give extra upload by amount of snatched
- Delay - do not allow low ratio users to leech new torrents
- Golden time - turn off delay and count download only a half
In addition, many users have tried to cheat the counting system. It is mostly impossible to prevent cheating due to BT protocol. That means tracker must track not only share ratio, but also list of who want to leech and who finished each torrent for cross checking.