The license allows to create and distribute copies of MathOverflow content, but it must be properly attributed. On the site you refer to, as far as I see, authors of posts are not mentioned.

@quid: At least in the last 10 days, from the post numbers I see no indication of a large number of deleted questions, and also there don't seem to be unusually many downvoted or closed questions such as to speak of an "attack". Or what do you refer to? -- Given what the moderators say, I would have thought it's something notably more serious.

Only users with at least 200 points are counted here. -- You are presently ranked 28th among 3108 ranked users, and $28/3108 = 0.0090 \dots$. This is where the "top 0.90% this year" come from, as far as I understand.

Concerning the visibility of visited links: I think you can make them look the same as unvisited links by switching off the browser history.

You can see your voting history at mathoverflow.net/users/4923/john-jiang?tab=votes. -- Though you won't be notified when answers which you upvoted get changed.