Independent analyst ICORating gave just 16% of major cryptocurrency exchanges a rating of A- or A with none at A+. Of the 135 platforms examined, Kraken (A), Coinbase (A), and Poloniex (A-) recieved the highest grades. 55% received between B+ and B- including Binance (B+) at 34th and the Winklesvoss twin's Gemini (B-) at 84th. ICORating based the ratings on four criteria: user account security, registrar and domain security, web security and DoS attack protection.