In a blog post published on Thursday, OpenSea said that employees of Customer.io had misused their employee access to download and share email addresses provided by OpenSea users and subscribers to their newsletter with an unauthorized external party.
Any customer that has shared their email with the marketplace - be it for the platform or its newsletter - is likely impacted by the breach. The NFT platform further warned users that this could result in "a heightened likelihood for email phishing attempts."
The NFT marketplace also said that it is now in contact with law enforcement officials over the breach and that an investigation is underway.
The latest data breach is the latest string of attacks on OpenSea this year. In May, the platform's Discord server was compromised and flooded with phishing attacks. Several user wallets were drained in the attack.
In January, the exchange saw one of its worst attacks to date, where an exploit allowed hackers to sell NFTs without the owners' permission. While the marketplace repaid about $1.8 million to its customers, the overall impact of the attack was unclear.