how http://blockchain.info/, http://blockexplorer.com/q or http://www.bitcoinmonitor.com/ works Possible Duplicate:
  How can I read information from the blockchain?  




Can anyone tell me from where exactly sites like 


http://www.bitcoinmonitor.com/ 
http://blockchain.info/
can't post more links


take their information.
How bitcoinmonitor knows what transactions have been done right now?
They monitor the public blockchain from multiple Bitcoin servers. There's a very simple rule for which chain is valid -- whatever chain has the most work is the valid one.