Infected don't change attack style for prone player positions.

In my testing a player with no gear can lay prone and avoid nearly all attacks from infected, irrelevant of the quantity of infected.
I did experience infrequent and minor hits when prone while carrying a mountain back pack, and on a separate occasion, the same minor injuries with just a fire extinguisher on my back.

In addition to the above, infected will only attack a player from the side when the player is prone.
They do not attack the head or feet of players that are prone.

As a result, if a player lays prone to an attacking zombie and points head or feet towards the infected, the infected will try to move to the players side, resulting in the player been pushed as the infected tries to move to the players side.
The player can actually use this to have the infected navigate them around terrain without using the keyboard and with no threat of injury.