How do i remove mac shield

Question

How can I get rid of this bogus MacShield?  It keeps wanting to scan my computer for virus's?

Answer 1

Congratulations, you got a trojan. Likely one of the MacDefender variants, don't give your credit card or personal information it's a scam.
If you did, call your bank or credit card company and freeze the card, get a new one issued.
Remove the malware
Quit the browser that you are using by clicking the red dot/blob/button in the top left corner of the window.
Delete the install package of "MacDefender" (or the other name variants) in your Downloads folder (or  the default folder set by your browser).
      Click Go on your menu bar and then click  Utilities.
Double-click Activity Monitor from the  Utilities window.
Make sure All Processes is selected in the drop-down menu at the top right corner of the window.
Select the malware by clicking the name "MacDefender" (or the other name variants) in the Process Name column.
Click Quit Process and click Force Quit if prompted.
Quit Activity Monitor by clicking the red dot/blob/button in the top left corner of the window.
Open your Mac OS X Applications folder by clicking  Finder  Applications.
Find "MacDefender.app" (or the other name variants) and drag it to the Trash and enter your administrator  password if prompted.
  For the MacShield variant, find "mdDownloader.app" and drag it to the Trash.
Empty the Trash by holding down the command key, right-click the Trash and and click Secure Empty Trash.
Search for and remove other files
Open a new Finder window by clicking Finder .
Under Places on the left-hand Sidebar, click your username. 
Double-click the Library folder and then double-click the Preferences folder.
Look for com.aplle.md.plist and move it to the Trash.
Empty the Trash by holding down the command key, right-click the Trash and and click Secure Empty Trash.
Use Spotlight (the white field at the top right-hand corner of the window) to search for the following terms and move any associated files to the Trash: "MacDefender", "MacSecurity", "MacProtector" or "Apple Security Center" or "MacShield"
For more information, visit the following Apple support  article (a bit outdated as new variants are appearing faster than the support article):
http://support.apple.com/kb/HT4650