This game has a really good gameplay loop and balancing! Games that are a bit frustrating and requires multi-tasking are usually not my favorite(because some are badly balanced), but this one balanced progress and setbacks perfectly.
For the viruses, my best solution is to drag them all to a corner. However, this made the dragging virus part of the gameplay a bit repetitive. I suggest to drag viruses to another place to take it out permanently, but spawning much more viruses to balance. However, the idea of a constant threat is a really great mechanic!
Great job!