and btw, here's the KB article we have at my place of work to deal with this:
Open Spotlight - type in Activity Monitor and click to launch the application
From the list of Process Names choose MacSecurity or MACDefender(dependent on version installed)
Click on the process to Force Quit and close the application
Download and install AppCleaner from http://www.freemacsoft.net/AppCleaner
Launch AppCleaner and drag MacSecurity or MACDefender from the Applications Folder over to the Uninstall screen in AppCleaner
Click Delete
Empty Trash and Reboot. (***Note: Be sure to empty the files from the Trash, as they will still launch if they are not emptied form the Trash.)
These types of infections can be acquired via SEO (Search Engine Optimization) attacks causing the user to be redirected to a malicious site by listing that site first in search results from a search engine (such as Google, Yahoo, etc.). These malicious sites then execute a Java exploit that allows the automatic download of a compressed ZIP archive. If this archive is then opened, then installer for the Rogue scanner starts.
To Help Prevent these types of infections by adding another layer that the user will need to go through to install:
Open Safari
Click on Safari on the top menu, choose preferences.
On the General Tab, uncheck the Box that lists "Open 'safe' files after download"
incredibly easy to remove.
Pretty good info... except for the part about using AppCleaner.
AppCleaner is just as likely to hose a Mac system as any malware. Just use Spotlight to find associated files, don't install any more crapware to "help".