My friend first got the blister because he was wearing new hiking boots on a 3 day hiking trip (a big no no!). After the blister formed his girlfriend accidentally kicked the back of his heel when he stopped short at one point and then became a bloody blister!
Some tips on avoiding blisters while hiking are:
Break in hiking boots prior to hiking
If you notice any friction anywhere on skin apply duct tape
Wear wool socks both in winter and summer
The big question…Should you pop a blister?
There really is no right or wrong answer. If you do decide to pop the blister make sure to apply something similar to Neosporin to the affected area and apply a band-aid as the area is no exposed to bacteria and possible infection once you puncture the skin.