Throw it in the bin SW treat it with contempt or at least keep and archive it - it sounds like a scam.... if it was genuine they would not mention the word, Porn, that is done to shame certain folk who could be unsure into paying -- Good tactic though. if it works for 10% of the letters they send out at random in the hope some will pay, it's a lucrative scam. ??
If in the unlikely event you receive further correspondence then that can be further checked out to see if it's genuine at a later time. ! The time for worrying about this one is, if you ever receive a genuine court summons.