Does anyone have a reason to sabotage your data? If there is not a good reason, it is probably some type of corruption or your host doing something weird. By default, MySQL doesn't do too much logging. I don't think records of each connection to databases is logged anywhere with any of the major control panels' default setup. You could try /var/log/mysql.log. Also check /var/log/secure for anything suspicious.
If someone else setup your MySQL server, you might just have a query log running.. the path would be in your my.cnf file (usually in /etc or /root).