If anything, the problem seems to start with incredibly lax risk management at this exchange.  According to the OKEX statement, the risk management team 'immediately' contacted the client to reduce the size of the trade - begging the question - how did their risk management system allow the trade to occur in the first place?  On the bright side, something like that should be easy to fix, but it is indicative, potentially of how many simple things are being overlooked in the rush to make money from crypto trading.

ProShare Advisors, pursuant to a separate Management Services Agreement, performs certain administrative services on behalf of the Funds, such as negotiating, coordinating and implementing the Trust’s contractual obligations with the Funds’ service providers; monitoring, overseeing and reviewing the performance of such service providers to ensure adherence to applicable contractual obligations; and preparing or coordinating reports and presentations to the Board of Trustees with respect to such service providers as requested or as deemed necessary. For these services, the Trust pays to ProShare Advisors a fee at the annual rate of 0.10% of average daily net assets for each of the Funds. ProShare Advisors has entered into an Advisory and Management Services Fee Waiver Agreement that waives this management services fee for the Morningstar Alternatives Solution ETF through at least October 31, 2018. Prior to this date, ProShare Advisors may not terminate the arrangement without the approval of the Board.
On 21 November 2017, the Tether cryptocurrency announced they were hacked, losing $31 million in USDT from their primary wallet.[89] The company has 'tagged' the stolen currency, hoping to 'lock' them in the hacker's wallet (making them unspendable). Tether indicates that it is building a new core for its primary wallet in response to the attack in order to prevent the stolen coins from being used.
•   Daily Position Limit Risk - Many U.S. futures exchanges limit the amount of fluctuation permitted in futures contract prices during a single trading day. Once the daily limit has been reached in a particular contract, no trades may be made that day at a price beyond that limit or trading may be suspended for specified periods during the trading day. In addition, these exchanges have established limits on the maximum amount of futures positions that any person may hold or control on such exchanges. These limits may restrict the amount of assets the Fund is able to invest in bitcoin futures contracts or have a negative impact on the price of such contracts. In order to comply with such limits, the Fund may be required to reduce the size of its outstanding positions or not enter into new positions that would otherwise be taken for the Fund. This could potentially subject the Funds to substantial losses or periods in which the Fund does not accept additional Creation Units.
In connection with its management of certain series of the Trust (i.e., the UltraShort S&P500®, the UltraShort QQQ®, the UltraShort Dow 30SM, the UltraShort MidCap400, the UltraShort SmallCap600, the UltraPro Short S&P500®, the UltraPro Short QQQ®, the UltraShort Basic Materials, the UltraShort Financials, the UltraShort Utilities, the UltraPro Short Nasdaq Biotechnology, the UltraPro MidCap 400, the UltraPro S&P 500®, the UltraPro QQQ®, the UltraPro Dow 30SM, the UltraPro Russell 2000, the UltraPro Nasdaq Biotechnology and the UltraPro Financial Select Sector) and the wholly owned subsidiary of each of the Managed Futures Strategy ETF, the Crude Oil Strategy ETF, the Bitcoin Futures Strategy ETF, the Short Bitcoin Futures Strategy ETF, the Blockchain/Bitcoin Strategy ETF, and the Bitcoin Futures/Equity Strategy ETF (i.e., ProShares Cayman Portfolio I, ProShares Cayman Crude Oil Portfolio, ProShares Cayman Bitcoin Futures Strategy Portfolio ProShares Cayman Short Bitcoin Futures Strategy Portfolio, ProShares Cayman Bitcoin Futures/Equity Strategy Portfolio and ProShares Cayman Bitcoin/Blockchain Strategy Portfolio, respectively) (collectively, the “Commodity Pools”) the Advisor has registered as a commodity pool operator (a “CPO”) and the Commodity Pools are commodity pools under the Commodity Exchange Act (the “CEA”). Accordingly, the Advisor is subject to registration and regulation as a CPO under the CEA, and must comply with various regulatory requirements under the CEA and the rules and regulations of the CFTC and the National Futures Association (“NFA”), including investor protection requirements, antifraud provisions, disclosure requirements and reporting and recordkeeping requirements. The Advisor is also subject to periodic inspections and audits by the CFTC and NFA. Compliance with these regulatory requirements could adversely affect the Commodity Pools’ total return. In this regard, any further amendment to the CEA or its related regulations that subject the Advisor or the Commodity Pools to additional regulation may have adverse impacts on the Commodity Pools’ operations and expenses.
Most swap agreements entered into by a Fund (but generally not CDS) calculate and settle the obligations of the parties to the agreement on a “net basis” with a single payment. Consequently, a Fund’s current obligations (or rights) under a swap agreement will generally be equal only to the net amount to be paid or received under the agreement based on the relative values of the positions held by each party to the agreement (the “net amount”). Other swap agreements, such as CDS, may require initial premium (discount) payments as well as periodic payments (receipts) related to the interest leg of the swap or to the default of the reference entity.

ProShare Advisors, from its own resources, including profits from advisory fees received from the Funds, also may make payments to broker-dealers and other financial institutions for their services and expenses incurred in connection with the distribution and promotion of the Funds’ Shares. In this regard, the Advisor or an affiliate of the Advisor, may directly or indirectly make cash payments to certain broker-dealers for participating in activities that are designed to make registered representatives and other professionals more knowledgeable about exchange traded products, including the Funds, or for other activities, such as participation in marketing activities and presentations, educational training programs, conferences, the development of technology platforms and
  •   The bitcoin exchanges on which bitcoin trades are relatively new and, in most cases, largely unregulated and, therefore, may be more exposed to volatility, fraud and security breaches than established, regulated exchanges for other products. Over the past several years, a number of Bitcoin Exchanges have been closed due to fraud, failure, security breaches or governmental regulations. The nature of the assets held at Bitcoin Exchanges make them appealing targets for hackers and a number of Bitcoin Exchanges have been victims of cybercrimes. No Bitcoin Exchange is immune from these risks. Fraudulent activity can increase volatility and have an adverse effect on the price of bitcoin, the general acceptance of bitcoin as an investment or means of currency and could have a negative impact on the bitcoin futures contracts in which the Fund invests and the value of the Fund.
The right of redemption may be suspended or the date of payment postponed with respect to any Fund (1) for any period during which the Exchange is closed (other than customary weekend and holiday closings); (2) for any period during which trading on the Exchange is suspended or restricted; (3) for any period during which an emergency exists as a result of which disposal of the shares of the Fund’s portfolio securities or determination of its NAV is not reasonably practicable; (4) in such other circumstance as is permitted by the SEC; or (5) for up to 14 calendar days for any of the Global Funds or Short or Ultra International ProShares Funds during an international local holiday, as described below in “Other Information”.
Cryptocurrency is based on knowledge sharing on a distributed platform. The entire transactional history is for everyone to see. One blockchain is one thread of transaction. One unit or one block stores many transactions. The size of the block is 1MB and generally stores around 1000 to 2000 transactions. The data entered cannot be altered, nor can it be removed, enabling a system of complete transparency and trust. The entire money flow for the working model is beyond the traditional practices of controlling tax rates, credit usage, and money supply in the market.
An Authorized Participant may place an order to redeem Creation Units (i) through the Clearing Process, or (ii) outside the Clearing Process. In either case, a redemption order for a Fund must be received by the following cut-off times (which may be earlier if the relevant Exchange or any relevant bond market closes early). In all cases purchase/redeem procedures are at this discretion of the Advisor and may be changed without notice.
In order to make sure that you actually have money in your margin account to settle the difference with Mortimer every day, you are required to put up an initial margin at the beginning of the contract. A lower sum, the so-called minimum margin or maintenance margin, is also defined by the broker. If the money in your margin account falls from the initial margin to the maintenance margin, it triggers a margin call: The broker requests you to fill up your margin account to at least the initial margin (of course, you may also put up more).
If you want to do scalping, then shorter-term expiree contracts that settle really soon would be fine. Keep in mind, the normal state of futures markets is "contango", which means that longer dated contracts will have a premium to the current spot rate, to reflect the interest rate differential and time preference.  This means you will see Weeklies maybe with a $1-2 preium and Quarterlies (assuming they expire months from now) with a $5-8 premium.  As an example we have Quarterlies contracts right now at OKCoin that settle on December 25. So we're just starting December now, that means that even though these are "Quarterlies" contracts by classification, they are expiring not 3 months from now, but 1 month from now. Don't mix up the settlement expiration date with the naming convention. 
As a result of compounding, for periods greater than one day, the use of leverage tends to cause the performance of a Fund to vary from its benchmark performance times the stated multiple or inverse multiple in the Fund’s investment objective, before accounting for fees and fund expenses. Compounding affects all investments, but has a more significant impact on geared funds. Four factors significantly affect how close daily compounded returns are to longer-term benchmark returns times the fund’s multiple: the length of the holding period, benchmark volatility, whether the multiple is positive or inverse, and its leverage level. Longer holding periods, higher benchmark volatility, inverse exposure and greater leverage each can lead to returns farther from the multiple times the benchmark return. As the tables below show, particularly during periods of higher benchmark volatility, compounding will cause longer term results to vary from the benchmark performance times the stated multiple in the Fund’s investment objective. This effect becomes more pronounced as volatility increases.

OmiseGO (OMG) is a public financial technology that’s based on Ethereum. The concept of OMG is to enable peer-to-peer value exchange and payment service in real time across not only decentralized currencies but fiat money as well. OmiseGO allows anyone on its network to process financial transactions (payrolls, B2B, remittances, payments, etc.) in a much more inexpensive and decentralized manner.
Non-VanEck proprietary information contained herein has been obtained from sources believed to be reliable, but not guaranteed. Not intended to be a forecast of future events, a guarantee of future results or investment advice. Historical performance is not indicative of future results. Current data may differ from data quoted. No part of this material may be reproduced in any form, or referred to in any other publication, without express written permission of VanEck.

Slippage is when the actual price we execute at is different from what we expect. In this case, a perfect market would let us sell the bitcoin and settle the future at precisely the same time and price. But in practice, market imperfections and Bitcoin volatility could lead to the price moving between the two trades, wiping out profits or putting you in the red.
As a shareholder on a Fund record date, you will earn a share of the investment income and net realized capital gains, if any, derived from a Fund’s direct security holdings and derivative instruments. You will receive such earnings as either an income dividend or a capital gains distribution. Each Fund intends to declare and distribute to its shareholders at least annually its net investment income, if any, as well as net realized capital gains, if any. Subject to Board approval, some or all of any net realized capital gains distribution may be declared payable in either additional shares of the respective Fund or in cash.
Since you bought 68.4246 BTC, you want to short 68 BTC and lock in the USD value. You will have 0.4246 BTC left over, which will give you a slightly long bias. You can either fix this by only buying 68 BTC in step 1 or by giving yourself more short exposure by shorting 69 BTC. Remember that CryptoFacilities contracts are inverse (which allow locking in USD) and are denominated in BTC