There is no way to be 100% sure, but I am wondering if this plugin has a vulnerability, as I've recently had a couple sites hacked where it appears this plugin might have been the problem.
Malicious code was inserted at the top of every php file in wordpress, the developer tools plugin was removed from the plugins list in the admin section, so it could not be seen, deactivated or deleted from the admin panel. Additionally, some folders/files associated with the plugin were set to 777.
Combined with the plugin's disappearance, it is setting off some alarms in my head.
I hope not, as I really like this plugin, but I've pulled it from all of my WordPress sites as a precaution in the meantime.