"Counterfeit" is probably a better word than "fake" to describe these problematic ICs. These parts will have an IC in them that will often be of the correct general type, but have issues such as (a) lower spec parts relabelled as a higher spec part by someone other than the original manufacturer, (b) factory rejects or seconds that someone else has acquired and placed counterfeit labelling on, (c) poorly made copies made by a "no name" company with counterfeit labelling, or (d) old parts recycled as new without testing. For commonly used commodity ICs being sold in large volume, there is money to made in that business.
