Cost Per Click Abuse

I ,being a newbie to this subject, have a friend that claims that his websites sponsored links have been abused by someone clicking on the links, possibly maliciously, and costing him a small fortune. My friend has an account with google and this is what is being abused.

I apologize if this is the wrong place to post this query however I would be grateful for help ‘steering’ me in the right direction so that I may find answers to this situation.