fry_forever!
Fish Herder
Although it is technically possible for a guppy / molly hybrid, I have kept those 2 fish together for many years and have never had it happen. The only likely way that it might happen would be if you only had one gender of each fish and no suitable mates otherwise for either fish. Even then it is not at all common. As far as a chance cross between the two, I would not worry about it.
Yes, oldman47 is right. I've never had the problem, though my guppy did try to mate with my molly once, and succeeded. That was only because he got confused, and he never did it again after.
P.S. I still have ich in my tank..... we'll see the outcome though.... =(
The temp is still up, and I put some more aquarium salt in, so we'll see what happens....
(Hopefully good news! )