Several users of Apple devices in Australia have reported that their gadgets have been "hijacked" - with a message demanding money.
Experts believed the hack had targeted users by exploiting the Find my iPhone feature.
A message appeared on some targeted phones asking for "$100 USD/EUR" to be sent to a PayPal account.
Mobile networks have advised affected users to contact Apple, which has not yet commented on the problem.
It appeared that the attacker gained access to users' iCloud accounts, the cloud storage service offered by Apple that is able to access devices remotely.
PayPal has said any funds sent to the specified account would be refunded.