I have read that the current authorization failures are due to an upgrade in the MW security features and that they were instituted to remove leechers. I think that there are a couple of simple things that can be done to increase security.

No.1 Stop selling to resellers. Not all but some sell the donation to more than 1 client which screws the client and the service

No.2 Stop letting people provide their own credentials i.e username, password serial no. Using a software generated set of credentials is fine but it should be done by the service provider and emailed to each client. In this way only the provider can change the credentials.