According to an anonymous Foxconn worker who spoke with China Business, Apple returned something between 5 and 8 million iPhones back to Foxconn over quality control issues, TweakTown reports.

The anonymous Foxconn worker said the issues are "due to the appearance of substandard or dysfunctional problems".

If the anonymous Foxconn workers claims are true, this would have cost Foxconn around $1.6 billion. This is also possible that the returned iPhones are thrown away, and aren't repaired or used to make another iPhone. There's no information on whether this applies to certain iPhones, or how far these quality control issues go, TweakTown says.