The affected phones were mostly sold in a 4-month period between September 2014 and January 2015, Apple said on its website.
The company, whose shares were set to open at their lowest this year on Monday, said a small component in the affected 6 Plus's iSight back camera may fail.
Read: Apple may launch next iPhone on September 9
Apple said it would replace the phone's camera free of charge if it takes blurry photos and falls into a particular serial number range.
Earlier, CNNMoney verified that a bug in Apple’s iOS has enabled a text message to shut down iPhones upon receiving the text.
The device merely needs to receive the text to shut the phone down and does not require the receiver to open it.
Read: The text that will make your iPhone crash
The text in the message includes two English words, a string of Arabic letters and one Japanese character, all of which appear to have no meaning.
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