This user received an upvote on every one of their eleven questions (and two of their answers), during a four minute window on November 14th. Three of those questions are closed, two have a negative score, and a further four would have a negative score if not for the upvotes in question.
Two days later, the user offered bounties on two of their questions, taking their rep down to a single digit.
What's the appropriate course of action here? The upvotes are clearly suspicious, but flagging each one individually seems like a waste of moderators' time. I've done a quick search for "suspicious voting activity" here on meta, but didn't find anything that suggested what to do in this situation.