Exmo, a cryptocurrency exchange headquartered in the United Kingdom, has suffered a major security breach causing the platform to freeze all withdrawals.

According to a security notice, Exmo detected suspicious withdrawal activity on Monday, with large amounts of major coins like Bitcoin (BTC) leaving the platform’s hot wallets.

Maria Stankevich, head of business development at Exmo, told Cointelegraph that the incident is “nothing very serious,” as the affected hot wallets comprise 5% of the total assets held by the exchange. “Let us stress that all the assets in the cold wallets are safe,” the announcement reads.

According to the announcement, other affected cryptocurrencies included Ether (ETH), XRP, Tether (USDT), Zcash (ZEC) and Ethereum Classic (ETC). The exchange mentioned correspondent crypto wallets that were likely to be involved in the hack, asking global exchanges to block the associated wallets.

Stankevich noted that the exchange has not yet calculated the amount of the losses, claiming that Exmo is now focused on tracking the movement of withdrawn funds.

Exmo launched a security investigation and also reported the case to the London police. The company asked users to not deposit any funds to Exmo wallets until the issue is resolved. “We want to assure you that if any user fund is affected by this incident, it will be covered completely by Exmo,” the company said.

Earlier in December, Exmo received a temporary registration from the U.K.’s Financial Conduct Authority, allowing it to continue trading for an extended period until July 9, 2021