Apple malware infections are relatively rare, although Mac users should not get complacent. New threats do appear from time to time and cybercriminals do target Mac users. This month another malware variant has been discovered – a type of screen locker – that is linked to a tech support scam and its Mac users that are being targeted.
The attack starts when the user clicks on a malicious link in a spam email message, although links on social media sites could also be used to direct end users to the malicious website where the attack occurs. When the malicious website is visited, malicious code on the site causes a denial-of-service attack which freezes the device as its memory is consumed.
The method of locking the computer depends on the version of OS X installed on the device. On older OS X versions, a visit to the malicious website will trigger the creation of multiple emails until the Macs memory is overloaded. The emails have the subject “Warning: Virus Detected”. Since no memory is available, users will not be able to launch any other programs. The email messages are only created as drafts – they are not delivered – although this will be sufficient to freeze the device.
Additionally, a message is loaded into the draft folder containing a phone number to call to have the virus removed. While the message appears to have been sent by Apple, this is part of the scam. This is how the attackers make their money. Removal of the infection will require payment. The attackers appear to be after credit card numbers.
The second variant of the attack affects newer OS X versions. Rather than trigger draft emails, a similar style of attack occurs via iTunes. Multiple iTunes windows are launched, similarly using up the Macs memory. As with the first attack, a message also appears with a telephone number to call to remove the infection.
These tech support scams may not involve any downloaded malware, although responding to this type of scam and providing credit card details will result in multiple payments being taken until the card provider blocks the card or credit limits are reached.
Tech support scams such as this frequently target Windows users via Firefox, IE, Edge or Chrome browsers. Multiple browser windows are launched with a tech support number displayed. A call is required to unlock the infection.
These browser-locking attacks are relatively common. Only last month, Symantec identified a new campaign which locks the screen on Windows computers and displays a browser window detailing imagery from the police force of the country where the user is based – Most of the attacks occurred in the US (FBI) and Europe (Europol).
Users are advised that they have been caught engaging in illegal online activity, usually related to pornography or child abuse. A code must be obtained from the police department to unlock the screen. A phone number is supplied which the user must call to make payment. The attackers rely on victims’ fear and embarrassment to obtain payment.