Buffer UNDERFLOWS: What do you know about it?

[Julio e2fsck Cesar <e2fsck () bol com br>]

Hi folks,

Well, this message is about a thing I thought very intersting. I've been
talking to a friend about buffers, when our monologue stopped in a unusual
kind of behaviour and few documented: buffer underflow.
I've been thinking about it for few days, Googling, looking for papers, articles
or whatever over the internet, but there is scant material about it.
So I decided ask what you guys know about it? What can be done exploiting this kind of flaw?
As most of you know, buffer overrun explores a boundary check of arguments, overflowing a memory region, in most cases 
leading to arbitrary code execution.
But what about underflows? What happens if I remove - pop() - more elements than a buffer has? Is possible to execute 
arbitrary code? Memory area dumping? Does it work only for stack or is it real also for heap? Or none? There are 
mechanisms to prevent underflows?
Well, I really need your expertise and skills for get out all doubts of my head about buffer underruns, once I don't 
have much knowledge in this field.
I really would like to thank Gustavo Monteiro for nights we stayed up talking bullshit and having fun, also for Lucien 
Rocha for our suddenly crafted monologues about computers :)
Sorry about any english mistakes.

Best regards,
Julio "e2fsck" Cesar
Recife - PE - Brazil
           san dimas high school football rules