From the e-mcat FAQ:
How long will my membership last?
We have two types of memberships. Our free membership is an unlimited membership, with the right to take Practice Test 3 as many times as you like. The purchased membership grants access to the practice test purchased, and you can take the test purchased as many times as you like. The paid membership is good for one year. The "clock" on your membership does not start until you activate your account.
They do have IP tracking, however, they're unclear about how many computers are covered. Furthermore, keep in mind that an IP address can give away someone's location. Considering this is the company that controls your ability to become a doctor, I wouldn't do anything stupid.