This is not a virus, and users must actually launch the app for it to install its payload. Once running, the app also asks which firewall port it can use. Trend Micro reports that "Mac users may be infected when they access remote websites hosting this backdoor. The backdoor may also be disguised as a legitimate application and may be installed and executed on systems."
Many Mac OS X-based malware seems to be similar in nature, requiring users to actually launch the installer and give it permission to install the payload. Unlike Windows-based malware, you shouldn't need to install any anti-malware apps to annoy you and slow down your Mac. Just make sure to follow the basic rules of Internet safety -- don't install applications that aren't legitimate or visit Web sites that you don't trust.
For more details, be sure to visit the Trend Micro Virus Encyclopedia.