As you've seen above, urban legends easily caught fire in a pre-internet world because of the lack of information out there. But urban legends have also spread far and wide BECAUSE of the internet.
A good example of an internet-era urban legend is the "butthole cut" of Cats, which people breathlessly talked about on Twitter, Reddit, and elsewhere. As it turns out, while the production never originally intended to make the cats, uh, that realistic, there was indeed a "butthole cut."
So, what's the story? It turns out that the digital effects team working on the movie was greatly overworked and under a lot of pressure. At one point, a source who worked on the film's visual effects told the Daily Beast, “We were looking at the playbacks; we were like, ‘What the hell? You guys see that?!’ We paused it, we went to call our supervisor, and we’re like, ‘There’s a fucking asshole in there! There’s buttholes!’ It wasn’t prominent, but you saw it."
The realistic cat backsides, it turns out, were unintentional and only ended up there because the animators were trying to make the cats look as if they had skin that folds as cat skin can. In the end, someone was hired to undo the mess.