This is the transaction.


Which is still unconfirmed.

I am trying to use https://coinb.in to create a double spend transaction with a higher fee but I am getting several errors such as:

18: txn-mempool-conflict OR 16: mandatory-script-verify-flag-failed (Script failed an OP_EQUALVERIFY operation)

How can I create a double spend transaction using https://coinb.in to block this attack?

In particular what goes in the transaction id field and the script field.

  • 3
    Looks like I managed to hack back my coins of the hacker by using electrum to do a double spend! :))) Dec 8, 2017 at 17:27
  • 2
    Don't share your wallet seed with anyone, and beware of any website that asks for your seed. That mybcdwallet website is a scam, see here: bitcoin.stackexchange.com/questions/63688/… Feb 13, 2018 at 18:52
  • Welcome to Bitcoin.SE! You can help the site by marking answers as accepted if they are correct and address the question so that the question does not remain as "unanswered".
    – Willtech
    Mar 24, 2018 at 23:28

1 Answer 1


So some background as to what happened here. I wanted to claim my bitcoin diamond air drop. I googled and this video came up first.

The video played this weird music which I think was hypnotic in some way. It instructed me to paste my blockchain.info restore phrase into this website: mybcdwallet.org.

I foolishly followed the instructions and did not realise at the time that I had handed over the restore phrase of my wallet to a hostile hacker. The next morning I woke up to find that a transaction had been initiated to transfer my bitcoins to another address (not owned by me!).

Fortunately the bitcoin mempool is clogged up with lots of transactions and the hacker used a small mining fee. Consequently the transaction had not been confirmed even though it had been initiated 10 hours before.

So what I did was installed Electrum wallet and restored my wallet into it. Electrum correctly assumed that I still had bitcoin in the wallet. I then basically did a "double-spend" i.e. I started another transaction of my own and sent the bitcoins to a paper wallet that I had created. I made sure that I used large mining fee to ensure that my transaction got processed before the fraudulent one.

The next morning I woke up to find that my transaction had been confirmed 13 times which means that I had taken back my bitcoin!

Lesson: Be very careful with your back up phrases. Don't type the phrase into a website you don't absolutely trust!

I'm not not sure if I can say the clogged mempool is a flaw of a design feature. But in this case it did save me a lot of money...

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