Hey,

i saw on https://en.bitcoin.it/wiki/Weaknesses that network can be attacked using multiple clients with different IPs, but i got problem anaylzing those two points:
* The attacker can relay only blocks that he creates, putting you on a separate network. You're then open to double-spending attacks.
* If you rely on transactions with 0 confirmations, the attacker can just filter out certain transactions to execute a double-spending attack.

Main problem for me is - how double spend attack will be performed? Isn't it working like that: when i download any block to my chain it is checked for double spends (checks are performed for every single TxIn) ? So even creating own blocks by attacker shouldn't allow that here..


Cheers,
Jakub