There is an abundance of anticaptcha key stealing software. Also there are lots of sites that sell anticaptcha keys. Given that we made a limit to the number of failed request attemps with incorrect keys.
If there are more than five failed attempts with different wrong keys, than IP is banned for 1 hour. Further attempts to send an image for recognition or check balance will ressult in IP_BANNED
Additionally you can select which ip addresses can send requests with your keys, which will provide you 100% protection from key theft.
At this moment our service constitutes more than 40% of russian anticaptcha market and there wasn’t a single offer to sell our keys. Means we are doing everything right.