It's odd because though the bots may have subscribed to the thread, the subscriptions would have gone with the accounts - so I'm not sure that deleting the thread will make much difference, but I will have a go at changing the ID of the thread and see if that helps at all. Deleting the thread is not an option.
This also appears to be the same group of \t\v\s spammers... whom I've been removing for the last few weeks.
//edit: cloned the thread (recycled the old one) - it might make a difference, but I seriously doubt it.
Just caught another \t\v\s spammer in the act as well...