We all use the internet for shopping, research, playing games social media but when is it an issue in work? If it stops you doing your job or you are visiting inappropriate sites then the employer has the right to invoke disciplinary action. Most of the time a quick reminder to the employee to reserve internet use to break time is adequate but on the odd occasion it may not be. It is really important to have a policy. which will lay out when use of the internet is appropriate and how company equipment or email systems should be used.
In the meantime best plan is to keep the cat videos to lunch time viewing.