Many companies outsource their payroll operations each having its own business

Many companies outsource their payroll operations each having its own business reasons for doing so. Smaller companies tend to process payroll in-house. In
this high-tech global business environment with information being shared quite freely is it a good idea for companies to process their payroll by internal
personnel? How can the employees of that company be ensured that their personal information is not being shared with others in the company? What legal
ramifications does the company face if immigration or protected class information is shared with others?