Can someone explain this double spend on blockchain.info?
Nothing malicious.  Two blocks were mined at the same time by different miners (Block 267647).  Both blocks included the transaction and both were broadcast to the network.  Both blocks show up in the block chain because you don't know who actually won until additional blocks are mined and added to one chain or the other.  The chain with the greatest amount of work done on it becomes the main chain and the other one gets orphaned.

This is why you need to wait for several confirmations before spending an output.  If you spent it as soon as you saw one of the blocks, your transaction could get rejected later on if the other block ended up winning.

You can tell this is what happened because the transaction ID is the same in both blocks.  In a double-spend, you would have two separate transactions attempting to spend the same transaction output.