My 2008 iMac, which has been extremely reliable for several years now, began to show the spinning 'beach ball' one day, and then would become unresponsive. After a couple of forced reboots, the internal HDD failed and would no longer start up. I had replaced it with a 1TB several years ago, so it was not the original. At the same time, however, the Seagate 2TB External Firewire HDD with Time Machine backups failed. When I booted from Snow Leopard, Disk Utility could not "Repair" either volume. A different drive connected via USB is OK. The biggest problem was that Time Machine never worked correctly, claiming some issue with the backup, so that I frequently had to wipe the TM volume and start again, so I had not run it in a while. How likely is it that both drives would fail? I am concerned about a virus or malware, though none was detected. It's terrible that both the backup and main drive would fail at the same time. My iMac and drives are on a UPS, so a power surge seemed out of the question, but maybe not? Since the iMac tends to run hot, I even have a Zippi fan on it, 24 hours a day.
Viruses or malware do not (generally) cause hard drives to fail. This was asked some time ago - so did you solve the problem in the end and if so, how?
For the record: Save the Console log files if this happens again. Using these files it is possible to limit the source of the problem to software or hardware issues. It is rather unlikely that two disks fail simultaneously due to independant reasons. Are you working in a hot or humid environment? Do your devices have surge protectors between them and the power outlet?