The basic Authorize.net module that comes with the oscommerce package has several problems. One of which is that it does not ask for the CVV number from the card holder. This contribution fixes that, as well as other, problems with the stock install. It does require Curl to be installed by your host (most hosts already have this installed but please verify first).

FREE INSTALLATION:
The installation of this module is free (For standard shops. For BTS shops the basic price will be deducted.), if you signup with our Authorize.net affiliate: http://www.freeauthnet.com/rates.html. The available rates are on that page. They are very competitive and it is unlikely you will find a better deal from another authorize.net reseller. To obtain this free installation, you must signup with the above reseller and mention to them that you were referred by us. The price of the installation will be refunded after 45 days of service or sooner if you are a previous customer of ours. Please contact us if you have any questions.