I couldn't agree with you more, unfortunately this is a common tactic. You may defend yourself against future occurrences by immediately "blocking" the perpetrator (online chess>>account>>privacy).

yes I completely agree.  it's unfortunate people have to be like that.

I do not understand what benefit that is to them. People are strange.

I frequently run into opponents who wait several minutes, apparently (or so one even told me!) so that I alt-tab to another program or browser window, not noticing when they later move, and subsequently win on time themselves.

Answer: they have nothing to lose.  They figure they've already lost, and there is the slim chance that, as the OP says, they might actually win if the other party doesn't pay attention.  I don't play live chess, so I've never come across this myself, but it seems pretty poor sportsmanship.

not to mention you may lose because your connection might fail, too

yep

One of the primary reasons I only play short games in live -- i.e. 5 minutes and under.  I want to mitigate the risk to my potential waiting time should I run into an opponent like this.  I don't dare leave an idle game unattended, because of the possibility of their making a move and running my timer down while I'm away.

No matter how you slice it it's a dick move, but since it's technically within their rights it's impossible to prevent.  My only suggestion is that a pattern of behaviour could be established retroactively for particularly regular abusers of this and punitive action taken based on that, but it would still be somewhat subjective.

the hate wait

This thread brings to mind my wondering how Spassky must have felt in 1972 in game 2 against Fischer, as he sat and stared at an empty chair and waited for Fischer's time to run out, not daring to leave, lest Fischer suddenly appear and begin play.

If sound is on you won't have to worry about alt-tabbing and doing something else in the meantime, unless there is less than a minute left remaining in which case every second counts. Or just start a new (long or blitz) game while the current one is pending. 

Happened to me regularly on yahoo, people hardly ever resigned, i,d win after 10 minutes by forfeit.

People do it to detach themselves from the reason for their loss.

They believe if they purposely lose on time in a lost position they can think of it as a "loss on time" instead of the real reason for their losing the game.

You could be playing someone like me who is actually looking very hard at the game trying to find a way out of the hopeless position I've put myself in. It may well look like I've wandered off but I'm there, thoughts racing with the speed of your average glacier.

 I was thinking of this though I'm pretty sure that's not what is being referred to here. I see the topic as being more along the lines of "you're about to deliver checkmate on your next move and your opponent just doesn't move and waits for time to run out"  I have one such game going on at the moment and it's not even live chess.

Issey: I've got my own pet theory on why some people do that in online chess. They seem to get overly attached to their rating points so if they think your rating is about to go up they'll take a smaller 'hit' to their rating if they hold off losing for a while. It's the only reason I can think of why they'd bother.

Upabushtrack, that theory makes a little more sense for turn based chess than live, as I imagine few players play simultaneous games in live.  The problem with it is that the risk of your opponent's rating going down undermines the rationale behind delaying the end of the game for this reason.  That's not to say that people don't do it, but it's likely a zero sum game on the average.

As for determining when (in live chess in particular) this behaviour is an opponent deep in thought versus abusing the clock, well, it's probably impossible to do programatically -- as I said above, your opponent is completely within their rights to use their time as they see fit so the risk of a detection algorithm punishing folks are are actually thinking a position through is probably a non-starter.  The key difference between the two behaviours, while still subjective, is in my mind spending a lot of time on a very difficult position (acceptable) versus spending a lot of time on a clearly lost position (likely poor sportsmanship).  Them problem is that even with the second scenario, the opponent could be legitimately thinking the position through because they don't recognize how lost it is.

Bottom line: I think it's completely unenforceable and as a result will always be an issue that people have to deal with.  Play shorter games and it won't be as big a problem when you have to wait one out.

Not only is it poor sportsmanship it does nothing to improve their game.

These are people who have little understanding of the difference between improving their game and improving their rating.  By artificially inflating their rating by the few wins they get this way, they've disconnected it from being a representation of their actual level of play and as a result have completely undermined any value it has.

I suspect the irony is lost on them.