The difference is that in the biological case the virus comes up by itself without the need for too much human intervention or 'source code". We already know that more then one group already managed to come up with a killer strain by (basically) just exposing the virus to ferrets in a cage.

A malicious virologist already knows enough to try to replicate the experiment in his own secret lab so censoring the information will just make it hard for the good researchers to do their job.