I have made some headway into our 'intrusive friend' and where they came from - and to assess the threat they pose.
I won't go into any details in a public post but additional security has now been implemented on the site to help prevent future such events happening, though this can often be a bit of a cat and mouse scenario unfortunately. It takes me back to the days where diarists were pretending to be other people and hiding behind anonymity while abusing each other. It's not somewhere I wanted to go back to - and to be fair I'm pretty satisfied that this isn't a regular user.
I would however like to remind those with public diaries or those leaving comments, that freedom of speech does not mean freedom from the consequences of that speech. If your speech spews hatred, incites violence or is otherwise illegal, we will co-operate with law enforcement agencies where-ever necessary. DearDiary.Net does not tolerate such things and never has. If this is to become a problem again then additional measures will be put in place to combat such crime as necessary.
For tonight I am leaving comments switched off. I will hopefully reinstate them tomorrow. It is obviously also time to consider moderation tools both for users and admins...
Anyway, to anyone who saw the offensive comments I apologise. I removed them as soon as I became aware of them and will do so again, so if they do crop up, please drop me a line.