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Looks like it was being exploited on Bytecoin

For example, these 2 transactions spend the output twice!

http://chainradar.com/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

http://chainradar.com/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Notice how the key image differs only in last 2 digits! That's because it's forged - ie 2 slighthly different key images for 1 output, allowing you to spend it twice by tricking the pre-patch node into thinking that both key images are valid for the given output. There can really be only 1 which can be checked only with a patched node, and one of those TX-es would become invalid.

Note that it's later patched in the code, but the patch applies only after Bytecoin block 1267000, so those double-spend transactions are still in the Bytecoin blockchain and have artificially inflated the supply.

Note that while I was writing this, those transactions mysteriously disappeared from chainradar block explorer! That doesn't mean that they're not in the blockchain (really, the only way to be sure is to run a Bytecoin node and check yourself if they're still there), but only that chainradar is not showing them. They can still be seen here (maybe they will disappear, too):

https://minergate.com/blockchain/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

https://minergate.com/blockchain/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Looks like it was being exploited on Bytecoin

For example, these 2 transactions spend the output 26e8958fc2b227b045c3f489f2ef98f0d5dfac05d3c63339b13802886d53fc05 twice!

http://chainradar.com/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

http://chainradar.com/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Notice how the key image differs only in last 2 digits! That's because it's forged - ie 2 slighthly different key images for 1 output, allowing you to spend it twice by tricking the pre-patch node into thinking that both key images are valid for the given output. There can really be only 1 which can be checked only with a patched node, and one of those TX-es would become invalid.

Note that it's later patched in the code, but the patch applies only after Bytecoin block 1267000, so those double-spend transactions are still in the Bytecoin blockchain and have artificially inflated the supply.

Note that while I was writing this, there were some problems with chainradar block explorer and those transactions disappeared for a while! That doesn't mean that they're not in the blockchain (really, the only way to be sure is to run a Bytecoin node and check yourself if they're still there), but only that chainradar was not showing them (seem to be back now). Just in case, they can also be seen here:

https://minergate.com/blockchain/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

https://minergate.com/blockchain/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Looks like it was being exploited on Bytecoin

For example, these 2 transactions spend the output twice!

http://chainradar.com/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

http://chainradar.com/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Notice how the key image differs only in last 2 digits! That's because it's forged - ie 2 slighthly different key images for 1 output, allowing you to spend it twice.

Note that it's later patched in the code, but the patch applies only after Bytecoin block 1267000, so those double-spend transactions are still in the Bytecoin chain and have artificially inflated the supply.

Looks like it was being exploited on Bytecoin

For example, these 2 transactions spend the output twice!

http://chainradar.com/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

http://chainradar.com/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Notice how the key image differs only in last 2 digits! That's because it's forged - ie 2 slighthly different key images for 1 output, allowing you to spend it twice by tricking the pre-patch node into thinking that both key images are valid for the given output. There can really be only 1 which can be checked only with a patched node, and one of those TX-es would become invalid.

Note that it's later patched in the code, but the patch applies only after Bytecoin block 1267000, so those double-spend transactions are still in the Bytecoin blockchain and have artificially inflated the supply.

Note that while I was writing this, those transactions mysteriously disappeared from chainradar block explorer! That doesn't mean that they're not in the blockchain (really, the only way to be sure is to run a Bytecoin node and check yourself if they're still there), but only that chainradar is not showing them. They can still be seen here (maybe they will disappear, too):

https://minergate.com/blockchain/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

https://minergate.com/blockchain/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Looks like it was being exploited on Bytecoin

For example, these 2 transactions spend the output twice!

http://chainradar.com/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

http://chainradar.com/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Notice how the key image differs only in last 2 digits! That's because it's forged - ie 2 key images for 1 output, allowing you to spend it twice.

Note that it's later patched in the code, but the patch applies only after Bytecoin block 1267000, so those double-spend transactions are still in the Bytecoin chain and have artificially inflated the supply.

Looks like it was being exploited on Bytecoin

For example, these 2 transactions spend the output twice!

http://chainradar.com/bcn/transaction/cef289d7fab6e35ac123db8a3f06f7675b48067e0dff185c72b140845b8b3b23

http://chainradar.com/bcn/transaction/7e418cc77935cc349f007cd5409d2b6908e4130321fa6f97ee0fee64b000ff85

Notice how the key image differs only in last 2 digits! That's because it's forged - ie 2 slighthly different key images for 1 output, allowing you to spend it twice.

Note that it's later patched in the code, but the patch applies only after Bytecoin block 1267000, so those double-spend transactions are still in the Bytecoin chain and have artificially inflated the supply.