Haha, I had the same idea. The since (valid) transactions are passed freely to all nodes in the Bitcoin network, one can just use the network as a signed messag

Haha, I had the same idea. The since (valid) transactions are passed freely to all nodes in the Bitcoin network, one can just use the network as a signed messaging platform. You don't need to query blockchain.info, all you need is a Bitcoin client that listens for incoming transactions. I've been writing an implementation on and off for a while now. The general idea is as follows: The botnet client connects to "n" Bitcoin nodes. If the same transaction is relayed by ceil(n/2) nodes, then we say that transaction is "confirmed" and examines the transaction to see if it's sent from botmaster's address (in fact we don't even have to use the botmaster's address, with BIP-0032 (https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki https://github.com/bitcoin/bips/blob/master/bip-0032.mediawi...), we can use related public keys) You don't even have to use transactions ("tx" messages), you can use the block messages if you are willing to tolerate an (on average) 10 minute delay, this would drastically reduce the network traffic sent/received by the botnet client. But these guys forced my hand, so I suppose I'll have to release what I have so far. The current botcoin client (c++11 with boost::asio) connects to the network, and gets transactions. Data extraction from transactions is unfinished. The current problem I'm working on is making sure that people cannot easily scan the Blockchain to look for c&c transactions. This can easily be done by encrypting the messages with a client specific key. However, I would like to have perfect forward secrecy, that is, suppose a sample client was obtained by researchers, past c&c messages should not be able to be decrypted (otherwise the blockchain contains a log of all of your C&C messages). [link redacted]