Szymon Woźniak of the Ministry of Finance made an official announcement on the legality of bitcoin on 18 December 2013 at a conference at the Warsaw School of Economics stating that the Ministry of Finance does not consider bitcoin illegal and does not want to hinder its development.  He clarified that while not illegal, bitcoin cannot be considered legal tender , and, in the light of the directives of the European Union, it is neither electronic money .  As of 27 January 2015, several banks have closed accounts of clients trading bitcoin, and indicated "presumption of criminal offense" as the cause, with "criminal offense" presumably being "cryptocurrency trade".  As of 7 July 2017, the National Bank of Poland ( NBP ) and Financial Supervision Authority ( KNF ) issued a comment on virtual "currencies".  They underlined that virtual currencies (including bitcoin): (1) are not issued or guaranteed by the central bank, (2) are not money, . they are neither legal tender nor currency, (3) can not be used to pay tax liabilities, (4) do not meet the criterion of universal acceptability in shopping and service points, (5) are not electronic money, (6) are not payment services (in legal terms), (7) are not financial instruments (in legal terms). They added that trading virtual currencies in Poland does not violate national or EU law, however, having virtual "currencies", involves many risks: (1) risk related to the possibility of loss of funds due to theft, (2) risk related to lack of guarantee, (3) risk of lack of universal acceptability, (4) risk related to the possibility of fraud, (5) risk of high price change. Because of these risks, the NBP and KNF warn against buying virtual currencies and investing in them. The NBP and KNF recognize that the purchase, possession and sale of virtual currencies by entities supervised by the KNF (. banks) would be burdened with high risk and would not ensure a stable and prudent management of the financial institution. Financial institutions should be cautious about engaging and cooperating with virtual currency "trading" entities.