Hong Kong-based cryptocurrency exchange Binance said it won’t resume trading or enable customer withdrawals until Friday amid a continued blackout blamed on a prolonged system upgrade.

The suspension has sparked fears that the exchange has been hacked, though Binance, responding to such comments on Twitter, has strongly pushed back against the claim.

According to the most recent statement from Binance, the exchange is expected to resume trading at 4 a.m. UTC on Friday.

“We will allow a 30-minute window where users can cancel open orders prior to trading being opened,” the exchange wrote. “We will continue to update every two hours until the upgrade is complete.”

The exchange first posted on Twitter about the trading outage on Wednesday, telling users that they may see some degraded performance for the duration.

However, two hours later chief executive Changpeng Zhao announced that a server issue caused data to fall out of sync, stating that the development team would have to re-sync from a master database. In subsequent tweets, Zhao said that the maintenance did not proceed as planned, prolonging the outage.

Binance first launched in the summer of 2017, and in recent months has become one of the largest venues for cryptocurrencies by trade volume. According to a December report from Tech In Asia, the exchange was seeing as much as $500 million in daily trading volumes at the time.

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Correction: This article has been updated for clarity.