URGENT HELP SECURITY BREACH WITHIN EXCEL!!

please can someone help asap. i run a very large school and the darlings have got an excel document that allows them to bypass some of our security and get pritty much free rome of the internet. i have included the macro content at the bottom. obviously i cant block excel or macros as they need them! can any one help me block this certain section of this feature?????

text from macro

Sub Show()
UserForm1.Show
End Sub

Sub Go()
UserForm1.WebBrowser1.Navigate (Sheets("Browser").Range("E5"))
UserForm1.Show
End Sub
Sub Google()
UserForm1.WebBrowser1.Navigate ("Google.co.uk")
UserForm1.Show
End Sub
Sub Facebook()
UserForm1.WebBrowser1.Navigate ("facebook.com")
UserForm1.Show
End Sub
Sub Hotmail()
UserForm1.WebBrowser1.Navigate ("hotmail.com")
UserForm1.Show
End Sub
Sub Gmail()
UserForm1.WebBrowser1.Navigate ("gmail.com")
UserForm1.Show
End Sub