Recently, we've been getting huge numbers of posts from similar-looking accounts about C programming. These users have now started answering their questions and upvoting each other: for example, this completely off-topic question was asked 40 minutes ago and has already received six answers; those answers and the question have a total score of +26. Here's another question with similar behaviour; they're also hijacking legitimate-looking questions.
What should ordinary users do in this sort of situation? Flag everything? Flag just the questions? Flag one post per user? Flag them as spam?