Fundamental securities analysis is not used by ProShare Advisors in seeking to correlate a Matching Fund’s investment returns with its index. Rather, ProShare Advisors primarily uses a passive or mathematical approach to determine the investments a Matching Fund makes and techniques it employs. While ProShare Advisors attempts to minimize any “tracking error,” certain factors tend to cause a Matching Fund’s investment results to vary from a perfect correlation to its index, as applicable. See “Special Considerations” below for additional details.
the price of Bitcoin and Bitcoin Futures Contracts. In particular, it is possible that the price of the Bitcoin Futures Contracts subsequent to a “fork” may be linked to the price of bitcoin on only one of the resulting Bitcoin Networks, rather than the aggregate price of bitcoin on all resulting Bitcoin Networks. The CBOE Futures Exchange (“CFE”) and Chicago Mercantile Exchange (“CME”) have announced different protocols for addressing forks.

Elaborating a bit on the concept of Cryptocurrency and the blockchain effect before we move onto the central theme. As put in words by Daniel Gasteiger on the topic ‘Blockchain Demystified’ at TEDxLausanne,‘A blockchain is nothing but a database, a database that is public, therefore not owned by anybody. Distributed hence not stored centrally on one computer but on many computers across the world. Constantly synchronized to keep the transactions up to date and secured overall by the art of cryptography to make it tamper proof and hacker proof. These four features make this technology exceptional.’ Daniel’s strong belief in the solidarity of the concept of Cryptocurrency motivated him to leave his full-fledged career of 20 years in financial services to focus on the concept of Blockchain. Looking to know more about how to formulate Cryptocurrency strategies? Read our blog on Cryptocurrencies Trading Strategy With Data Extraction Technique. 
Note that any losses on the bitcoin position is offset by the short position in the Jan XBT Futures contract.  Because Jan XBT was trading at a $1,000 premium to spot bitcoin, the profit for this trade is equal to that difference.  Now, keep in mind if bitcoin doubles between now and January 17 settlement the maximum profit is $1000.  Larry is giving up some upside to assure a return of $1000.
The term altcoin has various similar definitions. Stephanie Yang of The Wall Street Journal defined altcoins as "alternative digital currencies,"[25] while Paul Vigna, also of The Wall Street Journal, described altcoins as alternative versions of bitcoin.[26] Aaron Hankins of the MarketWatch refers to any cryptocurrencies other than bitcoin as altcoins.[27]
  •   Intellectual property claims. A proliferation of recent startups attempting to apply blockchain technology in different contexts means the possibility of conflicting intellectual property claims could be a risk to an issuer, its operations or its business. This could also pose a risk to blockchain platforms that permit transactions in digital securities.
Options give the holder of the option the right to buy (or to sell) a position in a security or in a contract to the writer of the option, at a certain price. There may be imperfect correlation, or even no correlation, between price movements of an options contract and price movements of investments underlying an options contract. Lack of correlation (or tracking) may be due to factors unrelated to the value of the investments being hedged, such as speculative or other pressures on the markets in which these instruments are traded. Consequently, the effectiveness of bitcoin options in providing exposure to the price movements of options will depend, in part, on the degree of correlation between price movements in the derivatives and price movements in underlying bitcoin markets. Exchanges can limit the number of positions that can be held or controlled by the Fund or the Sub-Adviser, thus limiting the ability to implement the Fund’s strategies. Options are also particularly subject to leverage risk and can be subject to liquidity risk.
There's a lot of ins and outs which can get confusing in arbitrage trading. We won't go into the technicals of why futures contracts trade at a premium to spot price. You can read a full explanation here. If it's not of interest to you, all you need to know is that there's a tendency, the further out in time the futures contract expires, for the premium to spot to be higher and higher in nominal percentage terms.