At the very least, you should be able to remove the invalid signature which will allow people to launch the app without turning off gatekeeper first. But I would of course prefer the code signature to be correct.
The new launcher appears not to be signed at all, which is an improvement over the previous state of affairs but still not ideal. I've attached the dialog that appears on my machine (and would appear on any other Mac running 10.8 still on the default security configuration) when you try and open the new launcher. The workaround is to right click the app and click "Open" which will give me the option to circumvent the security check.
MacRae Linton
MCL-124
At the very least, you should be able to remove the invalid signature which will allow people to launch the app without turning off gatekeeper first. But I would of course prefer the code signature to be correct.
Where can I get the new launcher from? I just went to minecraft.com and downloaded the zip file there and it still has this problem.
Warning for new launcher
The new launcher appears not to be signed at all, which is an improvement over the previous state of affairs but still not ideal. I've attached the dialog that appears on my machine (and would appear on any other Mac running 10.8 still on the default security configuration) when you try and open the new launcher. The workaround is to right click the app and click "Open" which will give me the option to circumvent the security check.
The only way to get a program to launch without hassle on OS X is to sign it with a developer key. (see http://support.apple.com/kb/ht5290 for more explanation of this OS X feature) It looks like the docs linked above may already be out of date, this appears to be the most relevant documentation on how to sign your code to avoid this dialog: https://developer.apple.com/library/ios/#documentation/IDEs/Conceptual/AppDistributionGuide/DistributingApplicationsOutside/DistributingApplicationsOutside.html#//apple_ref/doc/uid/TP40012582-CH12-SW2