[Ignore this post unless you're concerned about singleplayer

[Kusaki]

I appear to have found a viable method of "Wallhacking" using the littleblocks mod. it's horridly easy to do as well. All you have to do is place a piston/stickypiston in a littleblock square and when you break it, you get something called an "Invisable block". it has no texture, but is an item, and when placed against another block, you can see straight through that, and any adjacent blocks!

EDIT: Scratch that,it appears this only happens in singleplayer with any redstone elements.