The South Korean cryptocurrency exchange Bithumb recently suffered a hack that resulted in the loss of approximately $30 million in a variety of cryptoassets. The theft has recently been linked to Lazarus, a North Korea-linked hacker group also accused of other attacks, including the WannaCry ransomware.

Here, we investigate the destination of the funds stolen from Bithumb, and how funds from such attacks are being laundered.

Tracing the Stolen Bithumb Funds

Bithumb’s “hot wallet” was reported to have been compromised on June 20th, 2018, allowing the attackers to gain control of assets including bitcoin, ether and golem, alongside a number of other currencies and tokens (detailed in the table below).

The stolen assets, as reported by Bithumb

Elliptic’s software combines publicly-available cryptocurrency blockchain data with a proprietary dataset of addresses known to belong to various entities, and transaction analysis capabilities that reveal further addresses belonging to these actors. We can use this software to trace where the attackers sent these stolen funds. Here we focus on the stolen bitcoin, but the same principles could be used to trace the other assets.

However, in order to do this we first need to identify which funds were stolen. Bithumb processes thousands of withdrawals every day on behalf of its customers, so we must distinguish the stolen funds from legitimate withdrawals.

Bithumb suspended deposits at approximately 00:53 UTC on June 20th, and immediately began transferring all of its assets to secure “cold” wallets to prevent further losses. We can therefore assume that the theft occurred soon before this.

Over the days leading up to the hack being disclosed, the fee paid on the vast majority of transactions from addresses belonging to Bithumb ranged from approximately 0.0001 BTC to 0.03 BTC, and was usually a value with several decimal places, for example 0.003961 BTC.

However, on June 19th the majority of these transactions switched to using a fee of exactly 0.1 BTC - a fee notable for its size and the fact that it only used one decimal place. This might indicate that these transactions were not regular Bithumb withdrawals, but instead represent the theft of funds. Over the 19th and 20th of June, 400 transactions of this type sent funds from Bithumb to a single bitcoin wallet made up of 70 addresses. This wallet received a total of 1,993 BTC from Bithumb - close to the 2,016 BTC reported to have been lost.

What happened to these funds? They all ended up at a single cryptocurrency exchange - more on this later.

So we have approximately the amount reported as stolen being transferred out of Bithumb, around the time of the hack in around 400 transactions using a fee amount uncharacteristic of typical withdrawals, all to a single wallet.

One explanation for this might be that Bithumb realized they had been compromised and were sending their assets to a wallet that they knew was secure. However, it seems unlikely that they would move these funds to another exchange, where they would no longer be under their control, as happened here. It is far more reasonable to assume that these transactions represent the funds being stolen by the hackers. A large fee may have been used by the attackers to ensure the rapid transfer of bitcoins out of the Bithumb addresses.

These “stolen” funds remained dormant in the suspected hacker’s wallet for over a month, before being sent to a cryptocurrency exchange called YoBit. The entire 1,993 BTC was moved into YoBit over 68 transactions, between August 2nd and August 6th. Such a pattern of deposits is often seen where an individual is seeking to circumvent an exchange’s anti-money laundering controls, including their transaction limits.

YoBit is a cryptocurrency exchange based in Russia that allows its users to exchange between US Dollars, Russian Rubles and a number of cryptocurrencies. Fiat currency can be moved into and out of YoBit using a number of payment processors, including Payeer, AdvCash and PerfectMoney. Bithumb was reported to be working with some exchanges to recover stolen funds, but it is not clear whether this was achieved for the funds sent to YoBit.

It therefore seems likely that most (if not all) of the bitcoins stolen from Bithumb have been sent to a Russian exchange, perhaps to launder them and convert them into other crypto-assets or into fiat currency.

Soon after the incident, the Bithumb hack was linked to the Lazarus hacker group. Threat intelligence company AlienVault described how the malware and delivery method likely used to compromise Bithumb had previously been used by this group in other attacks. This would not be a new tactic for Lazarus: they have been implicated in a number of South Korean cryptocurrency thefts, including $7 million previously stolen from Bithumb in 2017.

Other cyberattacks linked to Lazarus include the WannaCry ransomware attack, an attack against Sony in 2014 and a $81 million Bangladesh Bank heist in 2016. Lazarus Group has itself been strongly linked to North Korea, with its tactics seemingly aimed at raising money for a regime crippled by sanctions. This was all but confirmed by the US Department of Justice, which released an indictment in September 2018 that attributed these attacks to agents of the North Korean government.

Without Regulation, Many Exchanges are Safe for Money Launderers

The Bithumb hack could therefore give us an insight into how North Korean agents may be laundering cryptocurrency obtained through cyber attacks. In this case the stolen bitcoins have been sent to a Russian cryptocurrency exchange, where they could have been converted into fiat currency or other crypto-assets.

Russia has been reported to have helped North Korea evade international sanctions in the past. A Russian exchange might therefore be a natural choice for North Korean cyber attackers to help them repatriate the proceeds of their activities. On the other hand, Yobit might simply have been chosen due to the weakness of its KYC and AML controls, making it easier to launder the funds.

Cryptocurrency derived from other attacks linked to Lazarus and North Korea has been laundered using other methods. For example, funds from the Wannacry ransomware were sent to exchanges such as the Switzerland-based Shapeshift, which did not identify its customers. This exchange was used to convert the funds into monero, a privacy-focused cryptocurrency that is much more difficult to trace than bitcoin. Shortly after the release of the US indictment implicating North Korea in the Wannacry attack, Shapeshift announced the introduction of customer identification requirements.

Many exchanges around the world still allow their users to convert between crypto-assets or into fiat currencies, while having little or no anti-money laundering procedures in place. Jurisdictions such as the United States, the EU and Japan have introduced regulation to compel certain cryptocurrency businesses to enforce measures such as customer identification and transaction monitoring. However, in most of the world such regulation does not yet exist, and so cryptoassets can still be exchanged and transferred relatively anonymously and untraceably.

Cryptocurrencies can be transferred across borders and over large distances with ease. Incidents such as the Bithumb theft and the WannaCry ransomware illustrate why regulation must be coordinated at a global level to ensure that the proceeds of cybercrime, including that perpetrated by nation state actors, cannot be laundered.