74LS161 binary counter negative spikes
Prototyping board uses to have a fair amount of inductance. Long wires too.

Any output that switches inductive load tends to ring and show voltage spikes.

Keeping components as close as possible in your prototyping board and short wires usually helps in reducing this effect.

If you then use perfboard and solder the components of  your prototype, you should see further improvements.

EDIT:

Also, check that your scope probe is well compensated. As Trevor says, they can easily show effects that aren't actually happening.