In the Graveyard memory level, get the glass jar, get the eight blue fireflies, give it to the statue, take the hammer. Now there are three crypts that you can smash open, in addition to the one to exit the area. Two of these optional crypts have zombie virus girls hanging out of sarcophagi. Go up to each of them and smash them with the hammer. (They don't die. You only need to do it once for each.)
Now go into the one that exits the area. (Code is "147".) Once you drop down and go up to the door, a cutscene will play. Once you regain control, hammer that door, and hammer through the next one! (Most of the doors here take about 8 or so hits.)
In the next room there will be two more zombie virus girls hanging out of sarcophagi. Bonk them each on the head with the hammer, just like the previous two. You'll probably die after each one as the walking zombie virus girls catch up, but that doesn't matter! Just get the other one the next time.
The fifth and final zombie virus girl in sarcophagi is in the next, identical room. Once you bonk her on the head as well, the achievement will unlock!
And just to clarify: You don't need to hit any of the zombie virus girls that are walking!