There is no limit to the number of credits you can earn overall, however, there are some daily limits in place.
You can click as many sites as you want each day, but you will only earn free credits on your first 250 clicks per day. We believe this is a good balance between preventing abuse, but also allowing you to earn lots of free credits.
The most credits you can earn per day by opening or reloading your TrafficSwarm Start Page is 30. This is to prevent cheaters from reloading the page 100s or 1000s of times and wasting the credits you and other users have earned. After 30 loads of your Start Page, you will need to click a link on the Start Page to earn credits. Again, you can continue to earn credits on your first 250 clicks each day.