As most of the companies, corporations are monitoring their employees closely, this is the trend which shows that monitoring employees is necessary and legal if you can consider all the employee monitoring related issues.
Here is an article link which will show you how to legally spy on your employees. You can consider it as tips and tricks of legally monitoring employees, but remember that the employee rights laws are different in different countries, so please make sure it is legal in your country to spy on employees by learning the details from your lawer.
How to legally Spy on Employees
From http://www.forbes.com/corporategovernance/2006/10/25/leadership-hewlett-packard-spying-lead-manage-cx_hc_1025fiveways.html
