"Ghost Mode"

[Barabajagal]

What about a router, then? Would that be a possible cause?

[tA-Kane]

iago is both correct and incorrect. Layer 2 indeed does not have any mechanism for deterministically dropping packets. It can, however, be instructed to drop packets by upper layer inspection mechanisms (though somehow I doubt that is the case).

What I do think is the case is that it could simply be regular packet loss which is resulting in this behaviour. TCP is supposed to automagically correct for packet loss. It would make sense that the end user might not notice anything abnormal (except maybe abnormally high chat latency) until the end of the connection -- at which point, there's no further information that needs to be guaranteed to be received by the other end. You can ask that user to monitor their route to Battle.net for high packet loss using Ping Plotter (JFGI).

Note that it's normal for some ISPs to have their routers not respond to pings at all (or when under high load), which would result in Ping Plotter determining that hop along the route to have (near-)100% packet loss. If you're still communicating with Battle.net just fine, then obviously that 100% packet loss would be incorrect. In my opinion, those ISPs are stupid fucks and shouldn't be service providers in the first place, but that's a different story.

In either case, if you do find a router that has abnormally high packet loss (more than about 1% is considered high), then you should contact your ISP about it. If the bad hop is further along the route, your ISP might not do anything and might tell you to contact the ISP that owns the malfunctioning (or misconfigured) router... and you should.

In the end though, if the user is honestly using a legitimate unaltered Blizzard client, then they shouldn't be having this issue.

[Barabajagal]

I don't talk to the person much anymore... She's been on once in the last 4 months or so (though I was able to recognize her by the fact that she got dropped from chat and was still in "USWest").

[vector]

Lol, that sounds like a MITM attack, but completely different concept, as there is no middle man involved.

As Andy said the client is disconnected from BNET once he leaves chat. I've been ghosted plenty times on Warcraft 3 to know that it also happens on there as well.

Why would modifying a packet prevent the client from properly logging off of battle.net?

[Pyro]

Why would modifying a packet prevent the client from properly logging off of battle.net?

Well, if the packet that notifies the server that the client has closed the connection isn't received properly by the server, it would still think that the user is connected.

[Kp]

I haven't checked in a while, but historically, there was a bug in the Blizzard clients that the SNP would not close the socket until the client unloaded the SNP.  Returning to the multiplayer menu is not sufficient to unload the SNP.  Returning to the main menu is sufficient.  I know this applied to Diablo, and it wouldn't surprise me if it affected the other clients, especially the legacy ones.