Today, October 2, 2012, a plugin named Newsletter Pro has been submitted to the WordPress Plugin Directory. By the way WordPress works, every user with a Newsletter Pro version installed will be prompted to update to a 3.1.9 version.
Who upgrade will loose its original Newsletter Pro version, since my plugin can be upgraded only downloading it from my site.
Thank you to the author of that Newsletter Pro plugin, surely he never thought about that, right?
Thank you to all who want to share this and help me on avoid that disaster!