That means your wp installation has been hacked. "Stack overflow" means some kind of programming has tried to access some part of the browsers functions and replied with a memory error. Most probably Javascript since it popped like an alert. You should check you theme to make sure it hasn´t been compromissed.

It's not even certain that your install has been hacked.

You have a LOT of javascript going on. Some scripts that shouldn't be there (contact form javascript, for one), facebook, you name it.

You'll need to try and recreate the error consistently, then you can start deactivating plugins and see if it goes away.

The half-techy explanation is there is some javascript running somewhere that is overloading IE's javascript stack limits. Kind of like an endless loop - but after a few hundred thousand times through the loop, the storage space gets used up.

Don't think internet explorer is running stack smashing protection...? So to say that the site has been hacked... If it had been hacked internet explorer would not be able to pop up a nice message. SteveJohnson is right, it's more likely a piece of javascript has got caught up in an infinite or very long loop. Run firefox with firebug or some internet explorer javascript debugger that picks out the exact line the stack runs out at. That'll give you an idea what plugin is causing it.

Hello...

In software, a stack overflow occurs when too much memory is used on the call stack. In many programming languages, the call stack contains a limited amount of memory, usually determined at the start of the program. ...