Such things happen most often due to the fact that your firewall or anti virus application is not activated. You should have them activated and also set your firewall to maximum security. The way that hackers act is simple, they search for weakly or not secured at all computers. Then they infiltrate the database and set a keylogger or other application working in background installed. The insformation is sent then every at an interval of time to their own computer.
Also, there are many friend requests that you should have been receiving. Always take care to see whom you add. In addition, there are many viruses that are sent through private messages, take care for not clicking on links that are sent in messages so quickly.
Kioskea FAQ provides the solution to your problem. Please access to it through the below link.