App Store download

I have downloaded OS X Yosemite and while trying to launch the installation I got a warning from Sophos Antivirus that "adware" was detected. Made the mistake to delete the download thinking that a new fresh download would be "clean".

Unfortunately my 'Purchased" list shows this item as "downloaded" (grayed out).

Is there a workaround which will enable me to download the software again?

Your suggestion and help will be greatly appreciated.