Quote from: kcsunshine on December 09, 2017, 01:17:09 AM

Quote from: Thirdspace on December 09, 2017, 01:12:18 AM

Quote from: kcsunshine on December 09, 2017, 12:46:02 AM

When someone is sending me bitcoin then, how do I detect a double spend before the transaction to me is confirmed??

by NOT acknowledging the transaction UNLESS it has received certain number of confirmations
some exchanges or services only credit user deposit after 3 or 6 confirmations for safety
in another words... you should never proceed your business before you are sure the tx is confirmed
even with 1 confirmation it could turn unconfirmed if it was rejected by the rest nodes on the main chain

Quote

Wait a minute. The transaction you show there that is confirmed, happened a day later. So I ask again (please no offense), How is it that the first transaction I show was sent back please. Look at the dates.

exactly... it is confirmed a day later while the earlier tx never got confirmation at all
so the latter tx is consider valid after a few confirmations and the earlier will be dropped and treated as invalid
its not about which one was sent out first but which one is confirmed first and accepted by majority nodes

WOW!!

So I do I detect from the beggining that a user is trying to rip me off??? How do I know he didn't send those funds to two wallets at the same time or something??? I need to know this because Ido a lot of bitcoin transactions.

To detect a double spend attack while the transaction has 0 confirmation. You have to check the network for additional transactions with the same unspent transaction output that can be spent as an input in a new transaction.

To prevent falling for double spend attack.
Wait for at least 1 confirmation before you finalize your trade, and the risk of double-spending is statistically zero.
Always be aware if someone sends you a transaction with suspiciously low fee.(which will probably never confirms)