Stocks of certain products disappearing automatically

We have about 2500 different products, but lately entire stock quantities of some products are just disappearing, turning into zero quantities, according to 'products_last_modified' when viewing in PHPmyAdmin, there is no manual updates done, stocks are apparently disappearing automatically, when we add the stock manually, the same thing happens again, it started with some products, mainly newly uploaded one, and it spreading to other products as well.

Any body can help with this? Thank you guys in advance.

Php version on site? (Admin window -> Version n upper right)

PHP Version: 5.3.29 (Zend: 2.3.0).

Lowwi:

PHP Version: 5.3.29 (Zend: 2.3.0).

What has changed on the site recently? (Ie. any new software installed?) Have you done a comparison of the files to a known good copy/backup?

Perhaps I misunderstood the above statement, but the field 'products_last_modified' is not an indicator of manually updating the database.

Is there any particular plugin that is installed that is "reserving" quantity of product and that actually the stock quantities could be accounted for by reviewing the stored carts of customers that have logged in?

While not necessarily the cause, performing the actions for a potential hack would likely provide some indication/information about the situation and be for good measure: http://www.zen-cart.com/wiki/index.php/Recovering_From_Hacks

Lowwi:

Any body can help with this? Thank you guys in advance.

Check your log files. They may provide a clue.

Cheers
RodG