uninstall sophos from my iMac

How do you remove Sophos when Apple will not open the removal tool because it cannot check it for malicious software. I downloaded it today! When I try to override the Apple security I get the following message: This software needs to be updated. Contact the developer for more information.

I have used Activity Monitor to Force Quit Sophos but still when i try to use Apple's suggestion of dragging it to the bin I get the message that it can't be moved to the bin because it is open.