Bitcoin Forum

I just saw a site called Bitundo (http://www.bitundo.com/). It allows you to basically "undo" transactions, double spending them (sort of). What do you guys think about this, you could easily be able to exploit some sites and users easily. Example, luckyb.it pays and sends back on 0 transactions, so you could use this service to get free bets correct?
I don't know how this works, someone please explain.

This site has to be fake right?

It appears to work on the premise that placing another transaction with higher fees for miners should entail that transaction is included in a block before the original transaction. BitUndo have then tried to monetize the process for their own benefit.

No harm would come if used against 0-zero confirmation gambling, as the process if successful would invalidate the first/gambled transaction and also any winnings from it, since the winnings are built using an input from the first (now invalid) transaction.

i don't think this will get much traction...

#1 you send TX1 without fees
#2 you quickly make another TX2 with fees and give it to them
#3 if they mine the next block, TX2 will be confirmed and TX1 invalid

Yes this can be exploited, but those accepting bitcoins will adapt (e.g. require 1 confirmation). For some scenarios this might be a good idea. E.g. a TX hanging in limbo for days because no fee.