What is the difference between "This area is infested" and "This area is overrun by monsters"?

Question

Sometimes when exploring the mine I see levels with high amount of monsters (primarily slimes). There are two different messages about such levels:

• This area is infested
• This area is overrun by monsters

In both cases you need to kill every monster on the floor to ladder to appear. So, what is the difference?

Answer 1

So, I was curious, and I've peek into the decompiled code.
It was found that there is no difference between this two messages. It just picks one at random to show:

Game1.showGlobalMessage(Game1.content.LoadString(random.NextDouble() < 0.5 ? "Strings\\Locations:Mines_Infested" : "Strings\\Locations:Mines_Overrun"));

Answer 2

I did a bit of searching and it seems that there's is no difference. Every site I come across says something like this : "If a level is "infested" or "overrun" by monsters, all enemies must be defeated on that floor before a ladder will appear" From the wiki, third line.

Another source: "For one, you may encounter a level that indicates it has been "infested" by monsters. On these levels you must kill every enemy in order to spawn the ladder." Guide to The Mines (Spoiler alert!)

It's just kill every monster and there seems to be 0 difference in "infested" or "overrun".

Answer 3

The difference is if an area is "infested" it has a much greater amount of monsters. If an area is overrun it has the same amount of monsters as an infested area but the monsters found here have a greater chance to be rare more powerful monsters. The actual amount of monsters varies little, but the specific type and power is determined by which message you see.