According to National Geographic, scientists in France have revived a "giant virus" originally extracted from the Siberian permafrost. It was found to still be active and able to infect an amoeba. The implications for this research point to serious concerns regarding global warming, as permafrost layers around the globe melt.
Giant viruses are so dubbed not only because they are larger and heartier than our "typical" viruses, but also because of the amount of genetic material that makes them. For instance, HIV contains only 12 genes, while this newly-discovered icky of the Pithovirus persuasion contains 500. That said, many in the field claim that such viruses have slim chances of infecting humans, as viruses are veeeerrrry particular in regard to who or what they infect.
There are three types of giant viruses: Mimivirus (which sounds like something my fiancee's grandmother invented), Pandoravirus (always a reassuring name), and the Pithovirus (the wittiest of the three virus classes). These three types lead virologists to surmise they actually evolved separately and that viruses do not necessarily share a common origin.
Essentially, the researchers are trying to determine what, if any, threat to humans may exist from these ancient viruses.