What constitutes an illegal alt?

One other occupant of the house I live in also plays Forumwarz from the same ip address, albeit hardly ever. Since we’re playing from the same home, does it count as legal or illegal?

I realise that this could sound like ‘I have an illegal alt but don’t want to admit it for fear of ruining my reputation’, but honestly, I don’t have that much of a reputation anyway.

Thanks!