Retracting CS (conference) papers
Correcting errors in conference papers is certainly possible---I have done so myself.  

Most reputable peer-reviewed conferences are associated with some sort of society or organization that maintains their archives, e.g., IEEE, ACM, AAAI, and that society will generally have a process for correcting or retracting their conference publications that looks much like their process for correcting or retracting the articles of the journals they maintain.

In many cases, however, a conference paper is superseded by a following journal paper, which effectively becomes the final and archival version.  In this case, while the authors have been less than honest about the flaw in their original paper, the later correction means that adjusting this particular paper in the archive is likely not a critical issue.