Even if you see a message displaying that "texmaker.app is damaged and can't be opened", it's not the case.
The package is not damaged (and there is no malware or viruses into it) : it's only Apple wich does everything to discourage users to install applications outside the appstore (and to force developers to pay to be certified).
To fix the problem, you can use this command (by replacing "/path/to" by the real path to texmaker.app):
xattr -dr com.apple.quarantine /path/to/texmaker.app
or
sudo xattr -dr com.apple.quarantine /path/to/texmaker.app
Some web pages talking about this current trouble on MacOsX :