Fast Facts

• Over 4 million Apple devices are vulnerable via abandoned digital calendar domains.
• Cybercriminals can inject malicious events, links, and files directly into users’ calendars.
• Bitsight researchers found more than 390 abandoned domains tied to iCalendar subscriptions.
• Attackers exploit social engineering, fake CAPTCHA pages, and disguised apps to lure victims.
• Current security tools barely monitor calendar channels, leaving users exposed.

The Silent Threat Lurking in Your Pocket

Imagine your digital calendar, usually a tidy grid of reminders and meetings, quietly turning into a hacker’s billboard - pushing phishing links and fake security alerts right onto your phone or laptop. According to a recent investigation by Bitsight, this is no dystopian fantasy but a reality for millions of Apple users worldwide.

Calendars: From Convenience to Cybercrime

Digital calendars have become indispensable, with many users subscribing to third-party event feeds for holidays, sales, or app reminders - often with a single tap. But this ease comes at a cost: when the domains hosting these calendar feeds are abandoned, they become low-hanging fruit for cybercriminals. By re-registering these domains, hackers gain the power to inject events - complete with phishing links, malicious files, or scam notifications - directly into users’ schedules, bypassing traditional email security entirely.

A Well-Oiled Cybercrime Machine

Bitsight’s team uncovered a sprawling infrastructure of more than 390 abandoned calendar domains, collectively receiving automated requests from about 4 million iOS and macOS devices. Many requests came from forgotten subscriptions - like old holiday calendars - still quietly syncing in the background. Once hijacked, these domains can distribute malware, phishing links, or intrusive notifications en masse, turning a simple calendar into a delivery system for cyberattacks.

The researchers also discovered a sophisticated network of hacked websites, misleading CAPTCHA pages, and disguised Android apps - all designed to trick users into subscribing to malicious calendars or push notifications. These attacks often hide behind .biz and .bid domains and are linked to notorious malware campaigns like Balada Injector. Even innocuous-looking PDFs can contain tiny URLs that secretly rope users into this web of deceit.

Why No One Saw It Coming

Unlike email, which is heavily protected by spam filters and antivirus tools, calendar syncing is often left unguarded - seen as a “safe” channel. Most mobile device management (MDM) systems can’t restrict calendar subscriptions or even show which ones exist. This security blind spot allows attackers to operate under the radar, delivering scams and malware directly into users’ daily routines.

Lessons from the Past - and What’s Next

This isn’t the first time digital calendars have been exploited. In 2019, Google Calendar users were hit with similar spam attacks, but the scale and automation of the current Apple-targeted campaigns are unprecedented. As our lives become more interconnected, attackers are quick to exploit overlooked corners of our digital world. The market for hijacked calendars could easily intersect with broader cybercrime trends - selling access to millions of devices, harvesting data, or launching targeted scams.

WIKICROOK

• iCalendar: iCalendar is a universal file format that lets users sync and share calendar events across different devices and calendar applications.
• Phishing: Phishing is a cybercrime where attackers send fake messages to trick users into revealing sensitive data or clicking malicious links.
• Domain Hijacking: Domain hijacking occurs when an attacker illegally takes control of a website address, often exploiting expired or unprotected domains for malicious purposes.
• Push Notifications: Push notifications are real-time alerts sent to your device by apps or websites, even when they're not open, to inform you about new activity.
• Social Engineering: Social engineering is the use of deception by hackers to trick people into revealing confidential information or providing unauthorized system access.