Playing jigsaw on my roof: They can ID you from your hygiene habits

Pat McGovern knew his way around a trash can

Something for the Weekend, Sir? Spies in space are watching me as I take a shower.

I know this because I have just now worked out where the weak link in my home defences lies: it's the boiler. My neighbours only have to lock their front doors and they feel safe. Me, I'm at risk every time I turn on the hot tap.

Perhaps I'd better explain. It all began with the office shredder.

Many years ago, Mme D bought one of those small electric document shredders you can pick up from stationery stores. It solved the problem of dealing with direct marketing letters that used to turn up in the post. We wouldn't want to drop them unopened straight in the paper recycling bin because direct marketing mail is highly personalised throughout with name, address, offer codes, customer numbers, and so on. What if naughty persons trawled through my junk mail at the recycling centre and found all this potentially lucrative data?

My paranoia about what goes into the trash began early in my professional career. Ha ha ha ha. (Sorry, referring to my working life as a "career" always makes me laugh.)

In my first year in my first real job, working at what is now IDG Communications, publisher of Computerworld among one or two others, the organisation's legendary founder and head honcho Pat McGovern came to visit our distant London outpost to big up our new magazines, rally the troops, and generally try to find out why we still weren't turning a profit. Once Pat had spoken to each employee individually – that was Pat's way: no group presentations, no speeches – our managing director duly took him out to lunch.

They were gone a long time, even for a business lunch, even for the double-breasted, shoulder-padded 1980s. When our MD eventually returned just as the rest of us were leaving the office, he was sober but frazzled. "He went through the bins!" he reported.

We were aghast. Our rubbish bins? Out the back? Did he see the rats? We had loads, big bastards they were, too.

"No, not our bins. Theirs."

It turned out that Pat had insisted on a post-meal drive around London to see where other computer magazine publishers were located in the city. Pulling up outside the office building of our main competitor, known at the time as VNU, Pat jumped out of the car and darted down the alley next to the building. Our MD found him behind the offices, going through the bins, looking for incriminating evidence of something or other.

"Bingo." He'd torn open another bin liner to find stacks of wide-carriage, dot-matrix printouts, all zig-zag continuous with horizontal green stripes and their perforated sprocket holes intact. Also intact on these printouts were VNU's internal financial reports. Bingo indeed.

So you see, I am not being overly cautious really. It's just that when I take the trash out the night before collection day, I don't want to find Zuckerberg rummaging around my paper recycling bin and Pichai sifting through the orange peel and coffee grains in the composter.

Breaking in through the front door is so passé. Smart guys find the back route, via your weakest link, the way in that you innocently leave unguarded. Our document shredder is supposed to shut down that particular back door.

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One thing Mme D and yours truly disagreed on in the early days of shredder ownership was what else should be fed into it. She felt that anything showing our postal address should be shredded. This, apparently, should include handwritten envelopes containing birthday cards from friends and family.

You're being paranoid, I told her. Our address is not a secret. The postman knows where we live for a start. Our neighbours know it too. A passer-by walking a dog down our street might randomly look up and notice our house; they would then know our address. An infinite number of monkeys with typewriters might, having polished off the lines …

As you from crimes would pardon'd be,
Let your indulgence set me free.

… suddenly decide to type …

47 Acacia Park Drive

Mme D calmly explained "jigsaw identification" to me for the first time, and I duly became as paranoid as her. We ditched the cheap wide-cut shredder for one that sliced documents into thinner strips. Then, over the years, we repeatedly upgraded: from cross cut to extra cross cut and then extreme cross cut. We're currently on absolutely bloody furious cut.

It's always the smallest things, the seemingly unimportant pieces of information that complete the jigsaw. Or the most innocent of data can be the skeleton key to your personal data. You only have to look at how something as harmless as a website favicon can be employed to persuade you to crowbar your own data to give you the jitters.

The fragility of it all impresses me too. It turns out that the American diplomats whose iPhones were compromised by NSO Group software weren't let down by the hardware or poor personal security measures. They could have avoided the whole problem simply by having a phone number beginning with +1.

So I can readily understand Kamala Harris's reluctance to use Bluetooth earphones. Bluetooth encryption is eminently breakable and those top-secret conversations are probably not worth leaking for the sake of one metre of cable. Me, I use Bluetooth earbuds all the time, but then I don't care if someone wants to deafen themselves by listening in on some industrial metal.

Unless …

my name + address + compost bin contents + industrial metal

= a "bingo" moment for a malicious actor. Yikes, I need a cold shower.

Ah yes, the shower.

Having gathered a billion pieces of nonsense jigsaw data that I selectively fed through to Ikea as a laugh, the flat-pack giant stopped trying to sell me squeaky furniture and began, somewhat ludicrously, sending me offers for installing photovoltaic panels on my roof. At a weak moment, I relented and sought a quote.

I discovered two things while getting that quote. Firstly, I found that it would take me nine years just to regain my return on investment: nine whole years before I could save a single euro on my bills.

Secondly, I realised that you can identify my house from space.

Sure, everyone can see their home in Google Maps' satellite view. But the quote process required me to identify mine and trace out the roof area. How would I recognise my own roof amid a row of identical townhouses?

Ah, I forgot. I have an old-school solar panel on my roof; one that heats the water in the boiler whenever it's sunny. None of my neighbours has one of these. You can spot my roof a mile off. About 1,000 miles upwards, in fact.

Conspiracy theorists and even town mayors here are convinced that the real-time usage data gathered by their Linky smart meters inform electricity suppliers when they are at home and when they are out. Well, thanks to a spy in the sky, the shape-shifters have snatched one more piece of the jigsaw.

name + address + industrial metal + it was sunny today

= Dabbsy's in the shower

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Alistair Dabbs is a freelance technology tart, juggling tech journalism, training and digital publishing. He shudders to think how bad actors out there will leverage the invaluable data gleaned from his showering history. On the other hand, times are hard and he wonders if anybody reading this would like to buy it from him direct. More at Autosave is for Wimps and @alidabbs.