The original “Effective Power” text bug from 2015 no longer crashes iPhones. Apple patched the vulnerability in iOS 8.4, and every iOS version since has included that fix. If someone sends you the exact string of characters that once caused chaos, your phone will display it as harmless text.
What the Effective Power Bug Actually Did
In May 2015, a specific string of text containing Arabic characters, the words “effective” and “power,” and a series of Unicode symbols could crash an iPhone simply by appearing in a notification. You didn’t even have to open the message. The notification banner alone was enough to trigger a reboot.
The problem sat in CoreText, Apple’s built-in software library for rendering text on screen. When the notification tried to display the string, a period character replaced part of an Arabic character that required more than one byte of storage. Normally, safety checks prevent partial characters from being stored, but this particular combination of characters bypassed those checks. CoreText then tried to access invalid memory, and the operating system responded by killing whatever program was running. Because the notification banner is a core part of iOS, that meant the entire system crashed and restarted. Opening the Messages app afterward triggered the same crash again, locking some users in a reboot loop until they found a workaround.
Why It Stopped Working
Apple released iOS 8.4 in June 2015, roughly a month after the bug went viral. The update fixed the CoreText rendering issue so the character combination no longer caused invalid memory access. Every major iOS release since then has carried that same fix forward. On any iPhone running iOS 9 or later (which at this point is every iPhone still receiving updates), the original Effective Power string is completely inert.
Similar Bugs That Came After
While the original Effective Power bug is dead, Apple has dealt with a steady stream of similar “text bomb” vulnerabilities over the years. The underlying principle is the same each time: a carefully crafted string of characters exploits a flaw in how iOS renders text, causing a crash.
- Rainbow text crash (January 2017): A message containing rainbow flag emoji and other characters could temporarily disable an iPhone.
- ChaiOS (January 2018): A malicious link pointing to a GitHub page crashed the Messages app on both iOS and macOS. It was widely called “the return of Effective Power,” though it worked through a link rather than raw text.
- Telugu character bug (February 2018): Two symbols from the Telugu language could crash iPhones, iPads, Macs, Apple Watches, and Apple TVs.
- Black Dot of Death (2018): An invisible Unicode character hidden after a black dot emoji crashed the Messages app when the message was opened.
- Sindhi/Italian flag crash (April 2020): A specific sequence of characters involving the Sindhi language and the Italian flag emoji could crash iPhones and iPads.
Apple patched each of these in subsequent iOS updates. None of them allowed an attacker to access your data or install anything on your device. They were nuisance bugs: annoying enough to force a reboot or temporarily lock you out of Messages, but not true security threats.
How to Protect Yourself From Text Bombs
Keeping your iPhone updated is the single most effective defense. Every known text bomb has been fixed in a software update, usually within weeks of being discovered. If you’re running the latest version of iOS, you’re protected against all publicly known variants.
Beyond updates, you can reduce your exposure by adjusting how notifications and unknown messages are handled. In the Messages app, tap the filter icon at the top right of your conversation list, then tap “Manage Filtering” and turn on “Screen Unknown Senders.” This routes messages from people not in your contacts into a separate folder and, more importantly, suppresses their notification banners. Since most text bombs rely on the notification preview to trigger the crash before you even open the message, this simple setting removes the most dangerous delivery mechanism.
You can also turn off message previews entirely. Go to Settings, then Notifications, then Messages, and set “Show Previews” to “Never.” Your phone will still alert you to new messages, but it won’t try to render the text content on your lock screen or notification banner. This is a useful precaution if you’re concerned about receiving messages from unknown numbers.
What to Do if a Text Crashes Your Phone
If you ever encounter a new, unpatched text bomb (they do still surface occasionally), the reboot loop is the main problem. Your phone crashes, restarts, loads the notification, and crashes again. The fix is straightforward: have someone else send a new message to the same conversation thread. This pushes the malicious text out of the notification preview and breaks the loop. You can also ask Siri to send a message to the person who sent the crash text, which accomplishes the same thing without needing to open Messages.
Once the loop is broken, delete the entire conversation thread containing the problematic message. Then update your iOS to the latest version, which will almost certainly include a fix once Apple becomes aware of the bug.