You'll receive your 100 FREE Credits when your referred user activates their account. Until then they will be reflected as a Non-Activated Referral in your stats. You will still earn credits when they open their browser, etc. you just won't get the 100 bonus credits until they activate their account.
This helps us to reduce cheating, and by giving away free credits only to those who are actually using TrafficSwarm (and their referer) we ensure that those who deserve it get the best results.