About a week ago I got a notice from WordPress.org letting me know Email Users had been de-listed from the plugin repository due to potential security exploit. While the odds were low, it was still a vulnerability which required fixing. This came at a time I was heading to Taiwan for work so my ability to fix it quickly was limited.
This morning I had some cycles to work on it while traveling home. I made the necessary fixes, committed them to Subversion, and informed WordPress.org. I just received a notice from WordPress that Email Users has been listed again. It may take a day or two to propagate through their cache.
Look for the version update notice on your Dashboard and I highly recommend installing this update. There is one other fix for users who use the Ithinx Groups plugin which had a bug in it.