An attacker discovered a vulnerability in the PDG software that would allow intruders to gain access to PDG shopping cart software installed on a retailer’s Web site and open the file that contained customer names, contact information, and credit card numbers. PDG developed a patch that its customers could use to repair the software the same day it found out about the intrusions. PDG posted the patch on its Web site so that companies using the software could download and install the patch. Both PDG and the FBI issued press releases immediately to warn users of the problem with the shopping cart software and encourage them to obtain the patch. Unfortunately, many users of PDG shopping cart software had purchased it as part of a complete electronic commerce Web site. These users were, in many cases, unaware that they were running the PDG shopping cart software.