In fact, one of referenced articles [0] states the students disclosed the hack to Ning in March. It's not clear when the hole was patched, but I have a hard time believing it has been nearly a month between the hack being demonstrated to Ning and Ning releasing a solution. Furthermore, it appears the Dutch news sites and TNW's translation are only reporting on the issue because the students are comfortable in now releasing this information, only after Ning has patched the vulnerability, BEFORE millions of accounts could be compromised. In this regard, I don't understand TNW's tone nor this post's title.
Of course, Ning should certainly come forward with their findings and what diligence was made.
[0] http://webwereld.nl/nieuws/110261/ning-lekt-accounts-100-mil...