Need Help With Infected External Hdd

Some time ago I was infected with a nasty worm that ate through my boot sector and just about everything else and I had to reformat everything. When it happened, I unplugged my external HDD and forgot about it. Unfortunately, I now need to access the backup data that is on it--if the worm didn't eat all that up!

My question: How do I safely open my external HDD and kill anything nasty that may be remaining on it? Should I boot in safe mode? Is there a program I can launch to kill anything lurking in it? I'm at a loss as to what to do.

Thanks for your help!