Verrucae are a virus, like a cold, they spread from one person to another. They can appear anywhere on the foot. They are also known as Planter Warts.
They do not spread easily, it is thought the easiest way is through swimming pools and changing rooms when your skin becomes soft and tiny cracks can happen.

They are quite different to CORNS that are caused by something rubbing against your foot the whole time, like trainers that don't fit.

They are not dangerous and if you leave them alone they will go away by themselves.

If they hurt a lot go and see a doctor, nurse, chiropodist or pediatrist who can treat them but the main advice is:
IF THEY DON'T BOTHER YOU DON'T BOTHER THEM!