Asos shares have tumbled after customers were told the online fashion seller’s systems had been “fully compromised” by hackers.

Users of the Asos app received a push notification on Tuesday morning titled “ASOS HACKED”, in an apparent attempt by the attackers to contact the company’s data protection and IT teams.

Asos is understood to be investigating whether any hack has taken place. Shares in the London-listed retailer fell by as much as 10 per cent following the apparent hack, to 439p.

“Dear ASOS DPO and IT, we have fully compromised the Snowflake instance”, the message read. “Engage with us, or we will leak it”. The notification included a link to a Telegram chat.

In a message posted on the Telegram channel, a user named “Xuanye Group” told users that customers’ payment information has not been affected. “That is all for now,” the apparent hackers said.

Snowflake is a cloud platform used to process data like clothing sizes and body measurements. This platform also allows the user to send notifications to clients’ phones.

It is not yet clear how the attackers were able to send a notification through the Asos app, whether its Snowflake systems were compromised as claimed, or how many customers may have been affected.

Apparent hack ‘brazen and threatening’

Reports of the notification emerged from users in several countries, including the UK, US, Germany and Australia. The incident could trigger reporting requirements if Asos confirms personal data has been compromised.

Under UK data protection rules, organisations generally have 72 hours to notify the Information Commissioner’s Office after becoming aware of a personal data breach where it poses a risk to people’s rights and freedoms. Those affected must also be informed without undue delay where a breach is likely to pose a high risk.

Marijus Briedis, the chief technology officer of online services provider Nord VPN, said the message sent by the apparent hackers was “unusually brazen and threatening”.

He added: “The attackers aren’t simply claiming to have breached ASOS – they’re publicly telling the company to engage with them or they will leak what they say they have obtained.

“What makes it even more concerning is how that threat appears to have been delivered. A message apparently written for ASOS’s data protection and IT teams has instead been pushed directly to customers through the company’s own app notification system.”

Asos has around 17m active customers globally and operates across more than 150 countries. The London-listed retailer has been attempting to revive its fortunes following several difficult years for online fashion, reporting revenue of around £2.5bn in 2025.

Chief executive José Antonio Ramos Calamonte had been making progress, with the group’s shares up by more than 50 per cent this year before Tuesday’s incident. Last month, Asos upgraded its pre-tax earnings target to between £150m and £180m owing to “materially improved profitability”.

British retailers have suffered a number of cyber attacks in recent years, with Marks & Spencer, Co-op and Harrods among those affected.

Asos was approached for comment.