Those who want to open an account and start trading on the Bitfinex cryptocurrency exchange will have to now provide an invitation code when registering. But Bitfinex did not specify who and how will distribute these codes.

Users paid attention to the new requirement when registering at the Hong Kong-based crypto-exchange Bitfinex. In addition to standard graphs, such as e-mail address, username and password, the platform now require an invitation code.

In the explanation to the graph the exchange says that "due to extraordinary demand, new accounts require an invitation code".

The exchange did not make any official statements in connection with the new registration rules neither in social networks nor a blog or on its website.

Users who failed to register on the exchange are trying to find out how to get the invitation code. But already registered users testify that they do not see any codes in their accounts.

In an effort to register at Bitfinex, one of the largest cryptocurrency exchanges in the world, some users declare their readiness to pay for an invitation code.

Bitfinex has often been a victim of DDoS attacks, but recently the exchange site has experienced frequent problems, resulting even in customers' assets loss.

According to CoinMarketCap, Bitfinex tops the rating of crypto-exchanges with a daily volume of over $4.8 billion, outstripping the South Korean cryptocurrency exchange Bithumb and the US-based Bittrex.

Earlier, the Bittrex exchange decided to suspend the registration of new customers "due to a large spike in new user sign-ups."