It seems like there may have been a delibrate 6 block re-org on Monero $XMR from Qubic mining. The target time is 2 minutes, therefore the re-org length is quite small. However, it is not clear if there was a double spend attack or if this was just selfish mining, i.e. trying to earn more of the block rewards. It seems for now that there is no evidence this was a double spend attack.
Qubic did seem to have around 20% of the Monero hashrate for a while and they may have sold some coins for USD, to rent hashrate to temporally push the hashrate up to over 30%. Qubic has significantly less than 51% of the hashrate, but perhaps it has just above the 33% theoretical threshold, where selfish mining is profitable (Assuming the coin price does not crash). It is not clear what the Qubic objective is here, but they do have a token $QUBIC and they may want to try and push up the price of it. Other than that, the endgame is unclear, but the "attack" from Qubic may not be sustainable
We have heard no reports of a double spend attack
@krakenfx@bitfinex@MEXC_Official
Any news on this? As for exchanges who take Monero deposits, it might be a good policy to increase the number of confs required for a deposit. source