Researchers in China have created a batch of designer viruses by selectively combining genes from the H5N1 bird flu virus with those of the H1N1 swine flu strain. This reassortment process — which can happen naturally in nature — resulted in several hybridized strains that were able spread through the air and infect mammals.
There is no evidence that H5N1 and H1N1 have ever mixed-and-matched genes on their own, but Chinese scientists are trying to get a leg up on the possibility. It's a similar strategy to the one employed by U.S. and Dutch researchers who deliberately modified the H5N1 virus into a human-contagious form. The idea is to know the enemy — and develop possible countermeasures — before it strikes. The danger/fear, of course, is that the virus could escape from the lab and wreak havoc in human populations.