Ubercart has recently released a security update that addresses a number of minor vulnerabilities as well as some more general improvements. We have applied this update to all Drupal 6 sites using Ubercart (i.e. all sites with e-commerce facilities).
If your site was affected, the update will not have changed your site in a noticeable way and you don't need to do anything to benefit from this. If you would like to know whether your site was affected, or more about how it was affected, please get in touch using the contact details at the bottom of this page, or the contact page on the site.