ASOS customers have been receiving pop-up messages from the app that appear to have been sent by hackers attempting to extort the company.
Dozens of people have informed the BBC about receiving a strange message from the clothing and beauty retailer's app on their phone screens.
"Dear ASOS DPO and IT, we have fully compromised the Snowflake instance. Engage with us, or we will leak it," the message reads.
Asos did not immediately respond to the BBC's requests for comment.
On social media, dozens of people have posted about receiving the message, confused about its meaning.
Although the apparent extortion message has been issued directly to customers, it is addressed to Asos' data protection officer (DPO) and IT team.
The message claims the unnamed hackers have "fully compromised the Snowflake instance".
It also refers to the data storage company Snowflake, whose popular tools have been used by dozens of firms for collecting, analysing, and storing data.
It is not known if ASOS is a customer of Snowflake or what data, if any, is stored with the service.
However, Snowflake has been the subject of many high-profile data breaches in recent years and has been linked to incidents targeting services including Ticketmaster and Santander.
