How do you ensure the security of employee data?

This can be done through several approaches, and securing Employees Data cant just be done through one process.  First, you need to ensure that whoever has access needs to sign a confidentiality agreement.  Second,  ensuring the people who have access are professionals who can be trusted with proper background checks and good track records of ethics.  In addition, the data that is accessed such as Employees Files should be securely located with no access zone to only one authorized HR personnel.  These cabinets should be secured with passwords and codes to access them.  On the other hand, Employees with access to System should be identified.  Regular checks on access roles of data should be done.  Above all, a secure place should be identified for Employees working on such data.  As you can see, it's a task in its self and great care and thought should be given to secure the confidentiality of data. 

ERP or HRIS (Human Resource Information System) software.

Securing your datacenter with firewalls and human identification access of logical and physical attendances, be sure of "Your wants and must do" in your system. Regular backing up the data and periodical passwords change, with appropriate network control software must do the job.

Through  HRIS(Human Resource information System)

For ensuring the security of employees data they must give the correct information for easy to access if theres something wrong happened