# Gavin Andresen
# 2011-03-17 19:56:40
# https://bitcointalk.org/index.php?topic=4559.msg66994#msg66994

@s{quotedtext}
@s{quotedtext}
 @p{brk}
They can only invalidate transactions that they made (or further transactions that spend transactions that they made).  That makes the attack a lot less likely in practice; if they had a lot of bitcoins, and purchased a lot of good or services (or exchanged them for dollars or euros) with a lot of people, then some of those people are likely to know WHO "they" are.  And if they're in the same legal jurisdiction, it seems to me you'd have a pretty good case for suing them for fraud. @p{par}

Even if 'they' decided to do this just to try to mess up the bitcoin network it might be messy for the exchanges to clean up but I don't think it would cripple them.  The bitcoin client already trys to select "old money" when it creates transactions, so assuming that the exchange has a good cushion of bitcoins on deposit all the attacker is likely to accomplish is to invalidate their own deposits at the exchange. @p{par}

All that said:  I'm not going to advise people to hold money they can't afford to lose in bitcoins until the network has a lot more hashing power.  There is still some risk while bitcoin is young. @p{brk}