Eugene's observations

The answer is that I don?t know.  Sometimes forensic examination can determine the cause but this is prohibitivley expensive.  There are several things that can cause corruptions but I have no way of knowing which apply in any particular instance.  An incomplete list of examples would be

• Virus action ? no security suites can be 100% effective, hence the importance of getting the best each year as they change that often
• Updates from Microsoft or others are often suspected of being culpable
• Hardware defects in the manufacturing process or sometimes just caused by too numerous thermal cycles 
• Users making adjustments can mess things up; including running programs that purport to ?clean the registry? or eliminate malware/adware/spyware/bloatware
• Bad coding and testing in an otherwise trusted program
• Electrical disturbances (surges, sags, brownouts, spikes) ? particularly if there is no surge protector employed, although this is less of a problem on devices that include their own electronic filters
• Physical jolts such as someone tripping over a power cord, dropping, or knocking the device
• Liquid ingress ? worse with sugar filled drinks and alcohol
• Junkware ? programs that are installed without the owners knowing consent typically advertising something and bundled in with wanted freeware
• Problems between two ?legitimate? programs that run into timing or locking conflicts
• Abrupt shutdown, perhaps by loss of power or the result of an earlier problem; in this case files held in memory are not flushed to disk.
• Fate