What did you hear about osCommerce and it not being secure?
I've used osCommerce many a times when I used to do web development, and had no security issues. If there are security issues, I'd love to hear them.
Also, I'm not sure if this CMS has shopping cart capabilities, but the talk of the town right now is Joomla -
http://www.joomla.org - check it out.
hth