Updated at 4:40 p.m. PDT with Google comment.
YouTube was busy deleting porn videos on Wednesday after users of forums at a rival site and an imageboard site declared a "Porn Day" campaign against the popular video service.
The forums at video site eBaum's World and 4chan organized the mass porn "carpet bombing" on YouTube, according to Ars Technica.
YouTube has been removing the videos as fast as it can, but even videos that are removed are still showing up in search results with explicit images in the thumbnails, the report said.
It could take a couple of days for all the explicit results to be removed from the search results, Google spokesman Scott Rubin told Ars Technica.
In a phone interview with CNET News late on Wednesday, Rubin said that in addition to the porn videos were removed as soon as community members alert YouTube to them, certain channels where the posters were bragging about the campaign and listing the videos were being disabled.
"This group of pranksters thought it would be funny to load a bunch of porn to YouTube," he said. "This is an unfortunate, and I think poorly directed, prank. I think our systems are doing really well at removing content that violates the guidelines."