It's doubtful that your SD card has been "attacked", but the files on there might be infected. It's more likely there's a virus on your computer itself that isn't allowing access to the device. Either way, I'd format the SD card, to ensure there is nothing left on it and then use the following methods to eradicate your system of any infections.
http://www.tomshardware.com/forum/8263-63-simple-free-guide-removing-malware
If you've already tried both virus and malware scans with no success, download and run the free version of Hitman Pro which is a second opinion scanner that catches a lot of infections or bits and pieces not caught using traditional scans.
I'd also go to malwarebytes website and download and run their free rootkit...