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Comment by cjg | Hacker News Reader

Calling on the official number is a good rule. But my neighbour followed that and was still scammed for tens of thousands.

The critical extra step that they missed was to check that the line was disconnected before calling out. They were using a landline.

The scammers called them, but didn't hang up. Then, when my neighbour called out to their bank, they pretended to be answering that call - going through security, etc.

My neighbour then did whatever the scammers said - because they couldn't possibly be scammers.

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For the people who are confused: this is a fairly common thing on landlines in some countries, where the telephone exchange doesn't drop the connection until both ends have hung up, or in some cases when the caller hangs up but not the callee. So it's possible to put your own phone down, but when you pick it up again your phone is still connected to the scammer's telephone. If they play a convincing dial tone, then change to a ring tone when they hear DTMF, you'd be none the wiser.

The workaround to this is to use another phone (e.g. switch to mobile), or if that's not possible, apparently you can wait several minutes until the exchange times out the connection.

https://security.stackexchange.com/questions/100268/does-han...

I accidentally won a radio contest many years ago in this way. I heard "you are caller 2" and then the DJ hung up. I stayed on because I was confused and then a few seconds later he picked up again and said you are "caller 4". So I just stayed on and eventually said I was caller 10 and the 10th caller won the prize. I assume he was switching back and forth between two internal phone lines.

I was confused because I was calling to make a song request and had no idea that this contest was initiated because they had just played a certain song.

I did that too, except I called the wrong number and won Barbara Streisand tickets. Not my jam.

Just FYI, this does not and never applied to mobile phones or any kind of entirely digital (SIP, etc) phone system.

Modern "landlines" when used with DSL or fibre are also no longer "true" landlines, instead the modem/router acts as a SIP client and gives you an FXS port to plug an analog phone into. While it could theoretically emulate this behavior (by keeping the SIP session open for a few more seconds), I don't believe any of them do - in any case it's trivial to test by calling a different phone that you control, hanging up on your "landline" and seeing whether the other phone hangs up immediately (it should) or if the line is held open for some more time.

If this is still a thing (I frankly don't see the purpose of it), it would only apply to real landlines where your phone is directly connected to your phone socket without a modem/router in between.

That's not necessarily true. Most smartphones and SIP clients are designed to kill RTP immediately after sending a BYE, but session teardown doesn't _have_ to happen then. There are many scenarios where a BYE would not constitute destruction of the RTP session, and using a dumb analog phone over FXP could easily be one of them.

Even already knowing about this I'm still mystified that landlines work this way on every occasion that I'm reminded of it. Does anyone know if there is, or at least was, a justification for this mode of operation? Was it at least of any use to anyone back around the 1900s or whenever or is it just another "we do it because that's how we've been doing it" residue that hasn't been cleaned yet?

Back in the day, folks would have more than one phone in their house.

Someone would call and all the phones would ring (or you might turn off the ringers on some of them so only one main phone actually rings). So someone might pick up the phone in the entrance hall and the caller would ask to speak to Becky, and Becky’s mom would yell up the stairs ‘BECKY PHONE’ and then put the receiver back down while Becky runs into her big sister’s room to grab the upstairs phone, and carry the whole phone, trailing on its wire, into her bedroom, slamming the door on the wire for privacy, before she picks up the receiver to answer.

I saw this sort of thing in american sitcoms as a child, and I was always mildly triggered by it. Here in Australia the landline phone system disconnects as soon as either person hangs up.

On the shows they would sometimes hang up the phone, then somebody else picked up a receiver and the call continued?? Phones don't work like that! Go try it on your real phone, and you'll see!

It never occurred to me that US phones worked differently than Aussie phones.

The fact I was so bothered by this probably says an awful lot about what sort of person I was as a child. Its no accident I fell in love with computers.

Just going from memory - but I’m fairly sure that around 25 to 30 years ago, in Australia, it did work the way that is being described. That is, the person receiving the call could not disconnect the call by hanging up. The person making the call needed to hang up, otherwise the line stayed open. I messed around with this a few times because I was amazed it existed.

Editing to add that more detail, since I’m basically contradicting your memory of how it worked:

I’m fairly certain it didn’t work if you dialled out, so you may not have come across the circumstances to test it. Also, the other person would probably also need to be participating in testing it, because otherwise they will hang up as soon as you do.

I’ve just remembered another detail - I think there was something different about the tone you heard. If you received a call, and the other person hung up, you would hear the disconnected beeps. If you made a call, and the recipient hung up, I think you would hear the disconnection, but then just silenced.

By the way - I was also confused by seeing how phones seemed to work in the US - like pushing the hang up sensors (is there a name for these?) once to switch lines for call waiting. I never really connected their strange behaviour with how the phones in Aussie worked.

Actually, is this all related to party lines? I’m fairly sure Aussie had these. NZ did.

Was harassment by exploiting this ever a big problem? Seems like you could call someone and if they pick up, you now control their phone line... indefinitely?

> you now control their phone line... indefinitely?

Some other comments said there was a timeout after which the call was disconnected if the receiver hangs up.

> On the shows they would sometimes hang up the phone, then somebody else picked up a receiver and the call continued?? Phones don't work like that!

Well, a few decades ago (80s-90s), at least, landlines sure did work like that in Australia, if you were the one who received the call. I played around with that a lot as a kid. Maybe you just tried it on calls you initiated?

Real phones did work like that in +61 20-30 years ago :).

I lived through this era and at one point worked at a phone company and never knew about this behavior. I'd hold the receiver until I heard the other person pick up, then hang up.

> and then put the receiver back down while Becky runs into her big sister’s room to grab the upstairs phone

This is dumb though. Just don't put it down until becky picks up.

"BECKY, PICK UP! I'm missing my show!"

As opposed to my sib comment, I could see (theoretically, not saying this is what the original logic was) some justification to deal with intermittent line breaks or connection issues - if one side can keep the call open, then a wind gust breaking the connection for a couple milliseconds somewhere between the two parties won't cause the whole call to end. From a customer point of view, it's more resilient and ends up with fewer dropped calls.

I could also theorize about the different switching actions going on, where up until the other party picks up there's already only one phone on the line, but that's getting into phone system/phreaking stuff that is way out of my depth.

Could this be related to party lines? https://en.m.wikipedia.org/wiki/Party_line_(telephony)

This is similar to the other answer regarding answering a different phone in the same house, but perhaps more necessary if sharing a line with neighbours. Distinctive ringtones may have made this phone line non-disconnection behaviour unnecessary though.

I’ve never experienced a party line - but they sound ridiculous (and fun).

If you're up for an (at least to me) fascinating rabbit hole of technological history in audio form, you might enjoy this narrated audio tour of analog phone switches:

https://www.evan-doorbell.com/production/group1.htm

I can confirm that at least once this happened to my family in Italy about 20 years ago.

The most anecdotal statement ever, but a data point nonetheless.

It even makes the news [0] periodically. Watch the video, especially 2:22-2:36 which reiterates the PSTN behavior.

[0] https://bc.ctvnews.ca/beware-of-the-delayed-disconnect-phone...

Was this common in the US? I spent a bunch of time on the phone in the late 90s at several of my family members houses (I was a social kid) and any time someone hung up I'm pretty sure I'd hear the busy signal if I left the phone unhooked long enough.

What the actual f. I feel like the only commenter here who wasn't aware of this. Thankfully I don't use landlines, but still, that is beyond crazy to me.

Back when I was in high school and landlines were still a thing, we used to prank our friends this way sometimes.

So your neighbor hung up to proceed with a follow up call, which, if they're like most people, consists in just pressing the switch with a finger, while keeping the handset to their ear. But then upon releasing the switch, they just started dialing without waiting for the dial tone? And after they finished dialing and never heard the ringing tone, they didn't find that unusual? Forgive my skepticism, but something's missing from that story.

Edit: Just read up on the disconnect time (10 seconds for some providers) and yes, a sophisticated scammer could indeed emulate the various tonalities.

scammer plays a dial tone after the 'hang up' and while dialing.

Was this in the UK? I think they dropped the timeout to help mitigate this. KNow someone else it happened to

The neighbor hung up, but the scammers didn't, and the call was not disconnected? That's not my experience. Is this what you meant?

Yes, and this is how it works as another responder mentions.

The thinking by phone companies is essentially: guy calling pays for the call, so we can milk each call for a few extra cents each time even if they're shady or a wrong number.

Apparently it is a feature Called Subscriber Held (CSH).

https://security.stackexchange.com/a/100342/143105

TL;DR It was just how analog phone worked, users came to rely on it, digital exchanges reimplemented it (with a timeout)

Your neighbor just dialed the new number without hanging up first?

Unless both sides hang up, there's something like a 10-20 second window where the call is held open. Hanging up, picking up within 10 seconds and dialing, means you're still connected to the original caller. If they're clever, the might even detect the click of you hanging up, and play a dialtone for when you pick back up, and stop playing it when you start to dial.

Citation needed. I don't recall any land line phone I've used behaving in this way.

I could see this working if the other end played a click followed by and dial tone sound.

No dial tone and no ring… Seems a difficult mistake to make but then again, I regularly surprise myself with my errors.

There's nothing technical that prevents the other side from playing dial tone and ring sounds

I guess we need to teach people how to use a phone line??

Your neighbour dialed a new number without hanging up his ongoing call? Is this his first time operating a telephone? The scammers mustn't have believed their luck when they realised that was happening. Did they mimic a "brnnnnggg brnnnggg" sound when he dialed?

> Did they mimic a "brnnnnggg brnnnggg" sound when he dialed?

Yes: https://bc.ctvnews.ca/beware-of-the-delayed-disconnect-phone...

Looks like you would have fallen for it.

The connection isn't always torn down immediately. Different switches behave differently in this regard. I remember a long time ago being trolled by a friend of mine who refused to hang up. I wanted to call someone else, but every time I picked up the handset to dial out, he was still on the line laughing at me.

So if you're served by a switch that operates this way, the scammer just holds the line open, plays dialtone and ringback tones appropriately, and you're none the wiser.

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