http://www.albinoblacksheep.com/flash/backmask/

Shows what you hear on some songs backwards I had heard of the Led Zeppelin and Daft Punk one before but I hadn't ever actually heard it play backwards. 

Do you guys think this is legit?  
I think it's true since I played Harder, Better... backwards after reading this and I heard exactly what they said on there.

I also heard somewhere that you're brain picks up the words when the song is playing normally even though you can't hear it.

Those things are most likely fake.

Someone sent me a reversed mp3 of "Stairway to heaven" before
he can actually write out the lyrics of the whole reversed song

But i'm skeptical to it

I know that in 70s, 80s, some bands actually did it intentionally, but just for fun

As AC/DC said, why the hell they need to encrypt the santanic message in backwards masking, since they are already singing them out in every songs

in case if you are interested

here is the backward version of "stairway" 

 ==============================

Plaaaay backwards,
Hear why its sung here, oppositioner..
Allll
on track, all arriving
They all sing, and they are one.
Shall I loathe you now, parishoner?
Oh hear Him, Christian within me.
It stirs my sin; the river,
Oh, she swells with our lousiness.
All my life will end for him?
We're all out of signs,
I know I'm sorta shocked
To hear The Lord,
My God now will save me

Oh I will n'er be saved,
Because I live with Satan..
One wish today;
That you'll all pray for
Three who will make it here late.
Pray now and you'll see..
The 'Lord' turned me on,
But, oh, I was the shaggy fool..
Clothed in agony,
Lost at a height.
ohh...
There's no escaping it,
Nor his woes..
So here's to my Sweet Satan.
The one whose little path
Would make me sad,
Whose power is fake.
He'll give those with him 666.
And all the evil fools,
they know he made
us suffer sadly.
Ohohohoh...
"Family won't get loose,
They've offered me."
Always soothes the worker.
All will be as we know now
"I see ruins," said he,
"the world they offered me?
Who wished the Lord's fall?"
If we lose feather,
Say you'll save me

And no wimps can bend the rules..
And no wimps can do..

Hunt next to the shore,
'Cause they see all from there,
See here's the news,
Who walks with mute grief
Perhaps no-one found thee...
"Heavy, lift me out,"
Spake the Reve,
"Someday, failed, we'll lose one line-up,
They've gotta leave forsaken."

And no wimps can do..
And no wimps can do...

He, who say the lords
Thoth have our laws,
Maat must be superb. Mass is ended..
Over there,
He who should learn thee.
Any moot?that serves by my sworn music,
I wish it with snow be shushed,
All for my mass's sake.
Hear why its sung,
here, oppositioner, Ohh..
He who should show
that make his show worthy,
To look, for us, odd.. sickly,
There's one chance - take his show.
Hold thy head,
Hear why its sung here. oppositioner.
Who owns this earth built below?
Oh sweet Israel..

 They're real...kind of.

You can make songs out of backwards lyrics and I'm sure there are people that actually do it/have done it, the problem is (as those above links show) are hard to understand.  You actually only really understand when someone tells you what the backwards lyrics are.  From that point onward your brain just finishes the words and makes them make sense.

 It's kind of like an optical illusion for the ears.

Listen to the Eminem one and then say that.

(Edit: But his is the least exciting backword lyrics.) 

in the 70s, 80s,
1) you can actually play a vinyl record in reverse direction, so some bands did it intentionally

2) backmasking was cool, because ppl related it to santaic in the past; if you happened to be a rock band, backmasking actually help your image

ever since CD replaced vinyl record, no one do the backmasking anymore.

I've always loved Another One Bites the Dust backwards. It's so funny.

There's also a Pink Floyd song with a hidden message in it. They told their fans that the first person to find the message would win a prize, and if you play the song backwards, around the middle it says something like, "Congratulations, you've found the hidden message! Contact ______ to receive your prize!"

People relate it to Satanism because the primary belief of a certain sect of Satanists is that all things are the opposite of what they really are, particularly in regards to Christianity. As such, when you play a song backwards (particularly Stairway to Heaven, in this case), you get the true meaning of the song (Stairway to Hell).

Satanists don't actually worship Satan.  They just believe that Christianity is a bunch of BS, and therefore push the opposite of what Christians believe just to rub it in their faces, in a way.

And no, I'm not a satanist.  I'm a practicing Catholic whose just done a good bit of research in the past, because I've often wondered why the satanists are what they are.

And there are some stories behind "Stairway to Heaven" too

1) Robert Plant bought Aleister Crowley' old house, who is a Satanist and wrote in reverse. And he left a lot of santaic stuffs in there

2) Plant wrote the that song in the house, so ppl related it to Satanic and backmasking

3) "Stairway to heaven" comes from their fourth album, which doesn't have a title, but represented by four strange symbols, many ppl think that those symbols have some dark eanings (But they have explained that those symbol has nothing to do with satan)

4) There is a freaky picture in the inside sleeve, looks like something from tarot cards

5) AC/DC have a album "Highway to hell", i think the title was inspired by "Stairway to heaven"