|Here's two more test websites. These give immediate results online:|
The second link also has a test that tries to exploit your machine.
It usually boils down to having a good firewall, preferably a router.
You should be aiming for stealthed (invisible) ports rather than just closed.
It is difficult to show whether you have already been exploited, short of
running a good AV, some AntiMalware programs and rootkit finders.
We all live on a ball.