A few of you may be wondering why nineteen questions just disappeared from the site. This meta post is meant to explain what just happened, and set a goal for how to handle similar situations in the future.
These posts were deleted because they were plagiarized. They were directly copied verbatim from other sources or websites. This is not acceptable for the Stack Exchange network. Copying or stealing others' work and claiming it as your own is ethically wrong, and devalues the work of others. In fact, since the source site had an explicit copyright notice, this could even be considered copyright violation.
The fact that many other users will also have their completely valid answers deleted is unfortunate. However, it is imperative that we set a certain standard of question quality, and plagiarism falls far, far below that quality line. This may seem unfair towards the users who have posted these answers, but it is necessary that no amount of copying or stealing from other sources can be tolerated. On a more positive note, this may encourage users to check for plagiarism more diligently (this specific situation went unnoticed for several weeks).
Moving forward from this particular situation, plagiarism is absolutely unsuitable for any Stack Exchange site. Please use an "other" flag on any copied posts you find, and they will be deleted promptly. After extensive discussion, a conclusion has been reached: Plagiarism is not okay, no matter what. Even if it means that legitimate answers have to go with them, plagiarized posts will always be removed immediately.
Please note that posts containing attribution are not plagiarized. They may be of low quality, but for them to count as plagiarism necessitates an absence of attribution.