That is lag
How do you report cheaters on Chess.com?

My son had something like that with kidchess a few days ago: his opponents clock suddenly stopped ticking, while his clock continued (also in the opponents time)... and he lost on time (with a lot of frustration for an 11 year old kid).
I thought it was a bug (on the IPad, Kidchess not always works smoothly), but when I read your story it seems more like a cheater.
Pitty

The Chesskid one must be a bug, and I see a lot of people complaining that their bad connection was their opponent cheating.

You' re probably right. It's no use to create paranoia -chess is a lovely game, maybe there are cheaters (probably with such a huge community), but they're cheating on themself in the first place.
I was playing ["naming and shaming" is not allowed here. mod] (1 September, 2013 @ ~ 3:00 CST, US) but lost, suddenly. Somehow, my opponent made multiple moves during a single, prolonged period --without my knowledge. Please forward this information to the appropriate person at chess.com. Thank you.
"Lag" would not explain how 3 minutes of time was ADDED to my opponent's clock and 3 minutes was SUBTRACTED from my time simultaneously. Again, I would like to know who I contact at Chess.com to report this individual player who likely commits this cheating against others besides just me.

I see you haven't been here long, so you haven't seen all the forums about this. There are many cases of this happening, and it actually is lag. if you don't see your opponent moving for awhile, reload the page, and the move, if they have made one, should show up.

It actually does explain the clocks.
Most people don't realize that the time shown on their computer is kept track on their own computer. Your computer thinks it's your opponents move, so it shows your opponent's time going down. The server and your opponent, on the other hand, thinks it's your move, so the official time is different than what your computer shows. When the server finally gets through and tells your computer the correct times, that's when you see the sudden shift.

["naming and shaming" is not allowed here. mod] played
494 games against fake acounts, he should be banned

But to answer your question in the title - to report (actual) cheaters, go to
http://support.chess.com/Tickets/Submit

StMichealD he is banned, Im really happy cos he cheated and only talk arrogance about himself. I disgust this kind of people. ( for any mistakes: I wrote to StMichealD and talk about G( should be C )MRyazan1 )

I played in a Blitz tournament recently and I had the white pieces I mad my move and waited. My opponent made no moves and his clock ticked down to the point at which he should have lost. Suddenly the clocks switched and I lost on time. I would definitely like to learn how to report cheaters on chess.com.

But he made no moves and yet the clocks switched how is that not cheating?
It may be a bug in the Chess.com programming. I had the same thing happen last week. I made my move. My opponent does not make a move for 14 minutes. I then get a message that I have lost on time, and when I check, I find that my opponent had over 14 minutes on their clock and I had none.
When I checked the game archive, I found that my move had not been recorded even though my computer showed that I had made my move and that my opponent's clock was counting down.
I submitted a ticket, and the staff are investigating.
Just curious if I can report cheaters on this site? I had an opponent let his time run down to 30 seconds, then he somehow changed the times, adding 3 minutes to his time and subtracting 3 minutes from mine. I lost on time with no recourse. This kind of behavior should not be tolerated or people will simply leave the site.