In this example, being asked for your username and password is totally expected. OS X always asks for a username and password when you try to install anything. Most users would have no reason to be suspicious.
Now I have a question for you. I use Windows 7 on my Mac through Bootcamp. Can I get infected by this or is Windows immune to all this OS X malware? I sure hope Windows is immune to this malware.
Apple has quietly added detection for the recent malware attack that used PDF files as lures to trick Mac OS X users into downloading a malicious Trojan dropper.
The detection was added into the rudimentary XProtect.plist malware blocker built into Mac OS X.
The malware, flagged as a trojan dropper, installs downloader component that downloads a backdoor program onto the system, while camouflaging its activity by opening a PDF file to distract the user.
However, in what has become a classic cat-and-mouse game, researchers have spotted a new Mac malware threat posing as a legitimate Flash Player installation package.
[ Researchers find Mac OS X malware posing as PDF file ]
Intego explains the characteristics of the new threat:
Users visiting certain malicious websites may see a link or an icon to download and install Flash Player. Since Mac OS X Lion does not include Flash Player, some users may be fooled and think this is a real installation link. When they click the link, an installation package downloads, and, if the user is using Safari as their web browser, the Mac OS X Installer will launch. (Safari considers installer packages, with .pkg or .mpkg extensions, to be “safe” files and will launch them after download, if default settings are used.)
If the user proceeds with the installation procedure, the installer for this Trojan horse will deactivate some network security software, Intego said.
After installation, [it] will delete the installation package itself. The malware installs a dyld (dynamic loader) library and auto-launch code, allowing it to inject code into applications the user launches. This code, installed in a file at ~/Library/Preferences/Preferences.dylib, connects to a remote server, and sends information about the infected Mac to this server: this includes the computer’s MAC address, a unique identifier. This will allow the malware to detect if a Mac is infected.
The company said it has spotted this new malware in the wild but notes that it is not widely distributed.
there's never been a way to make hard-headed mactards accept the truth that "Nothing made by man is indestructible by man" 
