warningsigns,
The double spending problem would not be a problem at all if everyone followed the advice of the creators of bitcoin and did not trust unconfirmed transactions. However, some web sites have ignored this rule in an attempt to increase their profits by not making users wait for transactions to confirm before providing them with a service (such as betting, crytocurrency exchange, etc.).
The Glass Hunt double spend site (
https://www.glasshunt.co/exploits/bitcoin-double-spend/) has been around for more than a year. All we have done with bitdoubler.io is to make a similar site that is open source, cheaper to use, and that has a lower minimum (so that users can risk less when trying out our site).
Peter Todd (one of the bitcoin core developers) has been advocating for an end to trusting unconfirmed transactions. He announced the success of his own double spend attack (
https://www.coingecko.com/buzz/peter-todd-explains-how-he-double-spent-coinbase) and even published its python source code (
https://github.com/petertodd/replace-by-fee-tools/blob/master/doublespend.py).
We are simply offering a service that works at the expense of others who unwisely trust unconfirmed transactions.