I'm not sure why news articles keep regurgitating the same untruths.
What’s worse is that cryptopia exchange do not admit it. This is not the way to solve this problem.”
Waht did they not admit ? It is published on their website.
https://www.cryptopia.co.nz/CoinInfo/?coin=AUAt least that article explains it accurately:
However, the fact is, AurumCoin lacked the hash rate to prevent a 51 percent attack
https://www.cryptopia.co.nz/CoinInfo/?coin=AUNote the date of the Cryptopia statement: 9 November
Check the date of the Aurumcoin website:
10 November:
https://archive.fo/iNLQa Cryptopia exchange was hacked, a total of 15,752.26 AU is missing from Cryptopia’s wallet
11 November:
https://archive.fo/cOcYFCryptopia exchange was hacked (51% attack), a total of 15,752.26 AU is missing from Cryptopia’s wallet. Aurum coin network is not the responsibility of anyone, same as Bitcoin network, it is open source distributed crypto currency. What’s worse is that cryptopia exchange do not admit it. This is not the way to solve this problem.
Whenever there is an issue there is an investigation and a report is made to the relevant authorities. This can take time.
I don't know what the amount of coins were involved but 15K of Aurumcoin was worth around $50K in October. Which is less than the cost of listing a new coin on Cryptopia.
Coins pay to be listed on Cryptopia.
Part of the listing criteria is their ongoing obligations:https://support.cryptopia.co.nz/csm?id=kb_article&sys_id=5d7482d2db9e9bc032a664a14a96199fIt includes:
You need to give us notice of the following:
Major issues with your coin, including hacks or network problems, as soon as you become aware of them.
https://cryptohub.online/ 80% of AU held by Cryptohub stolen
This stolen AU could have been used for the 51% attack.
https://bitcointalk.org/index.php?topic=1165615.1240 Did Aurumcoin inform Cryptopia of previous 51% attacks ?
Is your protocol and consensus mechanism secure? We may decline coins we think are vulnerable to 51% attacks.
Be aware of our delisting policy and your ongoing obligations:
Cryptopia reserves the right to remove any coin listed in its exchange markets for violations of our listing terms. This is solely at our discretion. Reasons a coin may be eligible for delisting include, but are not limited to:
Any network issues or vulnerabilities that could be exploited. Examples include:
Low hash-rate.
Reason to delist:
https://support.cryptopia.co.nz/csm?id=kb_article&sys_id=b8aa010ddb452b80d7e096888a961934The following criteria are required to be met by coin projects at the time of the listing:
Active and visible development team with at least two contacts given to Cryptopia (Lead Developer and CEO or Marketing Representative).
Below is a list of factors that are being constantly reviewed by our Cryptopia Service Delivery Team that may result in a token/ coin being delisted:
The token/ coin no longer meets our listing criteria.
A loss of, or poor communication between coin teams and our Cryptopia Listing Team.
Project is abandoned, *e.g.: No visible coin team, no working block explorer, no active updates on code repo, or no working website.
The token's/ coin's blockchain becomes compromised or there exists a possibility to be compromised based on hash rate, namely a 51% attack.
Disclaimer: I am not Cryptopia staff. I am a volunteer moderator for their trollbox and discord channel and user of their services. Cryptopia does not have staff that answer questions on Bitcointalk as it is not recognized as an official communications channel. I am not authorised to provide any statements on behalf of Cryptopia. This is personal opinion only.When a 51% attack occurs it means that the coin blockchain is neither immutable nor decentralized.
When a 51% attack occurs the transactions that occur and the blockchain mining is entirely controlled by the attacker.In order for a 51% attack to occur the blockchain (which is coded by Aurumcoin Developers) provides confirmations that appear on the block explorer which is provided by Aurumcoin (part of the listing conditions) which are produced by the nodes (which use the code produced by the Aurumcoin developers). These confirmations are then accepted by the wallet code (which is made and provided by Aurumcoin). These confirmations are later rejected by the Aurumcoin network and orphaned. The transactions that now make up part of the blockchain were privately mined and not broadcast publicly. It is a clear exploit of the Aurumcoin Blockchain.
A coin network can prevent a 51% attack by:
Providing sufficient mining reward.
Utilizing a hybrid POW, POS network (or masternodes).
Making the algorithm that is ASIC resistant to make it difficult to rent sufficient hashrate to perform an attack.
Introducing checkpointing.
Utilizing other technical solutions.
An exchange can prevent a 51% attack by:
Not accepting any deposits / de-listing a coin.
An exchange can make a 51% more difficult by:
Increasing required confirmations to over 200 confirmations
(More confirmations will just result in longer / more costly attacks)
Time-locking user funds so they cannot withdraw it from the exchange.
I explained it here:
51% attacks explained 
