Backup your data and rotate your backups and run Check Books frequently to detect problems.
In regards to what causes corruption of data:
1. Some process or program has added or removed information to the datad.nv file.
2. The Hard disk is badly fragmented.
3. Computer Memory / Windows.
4. Hardware failure.
The list could go on but the best defense against losing data is to backup frequently rotate your backups, and to run Check Books to detect problems.
Regards to All,