I wouldn't recommend using these sites for checking your ports as they don't seem to work properly for some people. (In my case they even claim that my http port is closed )
There was a small freeware-tool available somewhere that did this better but i can't seem to find it atm.
No, we don't and it's really not our resposibility to do so.
Let me put it this way: MTA is just about as safe as any other commercial game that you play every day and surfing the internet with a common (and possibly outdated) browser is probably way more dangerous than playing MTA.
That's just what Towncivilian did.
Every new line in his qoute represents another anti-virus engine that checked MTA and out of so many only one (McAffee) reported it as an actual virus.