http://www.whizlabs.com/faq/index.php?p=default&cat=7#a7
How many machines I can install the exam simulator on?
You can install Whizlabs Exam Simulator maximum 3 times on same machine or different machines. As we understand the need of a person to re-install it, say for use at home and work or for times of eventuality like system crash or reformatting, Whizlabs allow 3 activations with the same license number provided to you at the time of purchase.
but ....
http://www.whizlabs.com/Lic-agreement.html
GRANT OF SINGLE-USER LICENSE.
YOU ARE THE ONLY PERSON ENTITLED TO USE THIS SOFTWARE. This is a license agreement between you (an individual) and Whizlabs Software Private Limited whereby Whizlabs grants you the non-exclusive and non-transferable license and right to use this software product, updates (if any), and accompanying documentation (collectively the "Software"). ONLY YOU (AND NO ONE ELSE) IS ENTITLED TO INSTALL, OR USE THE SOFTWARE. .....
Jacek