I should mention that when I check with Tweepi and ManageFilter, and I have done so several times, none of my followers have unfollowed me. If there is a problem with spammers then those must be the followers sent by twitter. I only follow those who I notice retweeting others tweet. I have just noticed that ManageFilter says that I have 10,502 followers and Tweepi claims I have 10,503.
I am not following any more poeple that twitter sends, it's hopeless. I will only followback those whom I follow..