One method would be to make a filter plugin. You could either set all posts from users under a certain number of points to be moderated (this can be done in the admin area actually), or do some custom filtering in a plugin. For example:
public function filter_question( &$question, &$errors, $oldquestion )
{
if ( strpos($question['content'], 'seonuke.info') !== false )
$question['queued'] = true;
}
If you want to avoid having moderation at all, you can also return a string from the function to show an error message to the user. So assuming it is a robot, then the question wouldn't get posted at all.
EDIT: oh god it's worse than I thought, they are in the business of explicitly spamming other sites... this is from their site:
Its a simple process - Our system automatically asks questions (You define, with spyntax!) on a random site from our database of over 5000+ targets.
Within a few hours, a second UNIQUE account comes back with a reply, and reccomends your site as the solution to the "askers" question.
ಠ_ಠ
