MTV Networks has acquired the remaining portion of Social Project that it did not already own. Social Project is behind the Flux social-networking platform that powers many of MTV’s sites, including MTV.com, TheDailyShow.com, and ColbertNation.com.

Social Project, which competes with Ning and KickApps to allow people to create their own niche social networks, had previously raised $47.5 million, mostly from MTV’s parent company Viacom. Flux has a total of 7.6 million members across about 1,000 different sites, 600,000 of which are at MTV.com alone.

Compared to other social networking platforms, Flux still powers a relatively small number of sites – 1000 vs. 475,000 at Ning. But the number of people each one reaches are not be so far apart. ComScore says Ning reaches 6.9 million monthly unique visitors worldwide, though that’s not an exact comparison to Flux’s 7.6 million registered users (not visitors).

Flux has one thing going for it that Ning doesn’t: MTV. Flux members can automatically bring their entire collection of videos and other content from MTV.com to Flux’s other sites. While it’s not clear what the mashup is between music videos and social networking, TechCrunch points out that it does allow Viacom to add media to its sites without having to rely on someone else’s technology.