It's doubtless a threat to Wikipedia, and a sustained one, but Wikipedia's well equipped to handle it. I spent several years as an anti-vandal editor; even back then editors had a huge and powerful suite of tools to quickly, easily, and accurately contextualise edits and revert them; I regularly checked several hundred edits an hour. Every edit is reviewed by a small army of diligent people checking facts, rephrasing contributions, and warning/banning offenders; it's less a question of if a mal-intended edit would be reverted, and more when it would be reverted (Generally in the first half-minute, rarely more than a few minutes) I stopped patrolling edits because I felt I was simply spending my time making an already very efficient machine only seconds more efficient; there were better things to do with my time.