I think we've had problems with spam from India. What normally happens is someone signs up, posts a load of meaningless, but not spam posts such as "Good forum", "Thanks for the information" etc. then starts spamming. Fortunately the administration team have recognised this pattern and will ban a user quickly when they spot it.
Sometimes they have to ban IP addresses because a spammer will just sign up with a new account. Unfortunately IP addresses are sometimes shared by many people with the same ISP, so if one user spams, they all get banned.