I feel sorry for any of your victims who eventually purchase and want to install software, and the tech support agents who take the call. The software won't install, the customer won't be able to identify the version of Windows, and the agent may never be able to identify the problem.

Perhaps you could identify common locations that are used to identify Windows versions and leave pointers to a text file explaining exactly what you've done. This would allow tech support to determine that the customer has been deceived and has wasted their money, and to point them back toward you for vengeance (and give you the chance to supply an OSS program that does the same thing for free).

These days I have have adopted a very aggressive attitude to 'correctional computing'

When a "stealth install" blows up in someone's face and you find yourself in court, you will have reinforced all the negative stereotypes of the Geek. God help you if actually try to collect that 120 quid from an "older person," a pensioner, perhaps, who wants his Windows system back in order as you promised.

So you're deliberately deleting a working, legitimate Windows install, replacing it with Linux against the wishes of the user, then (when they complain) trying to charge then £120 for another version of Windows, because you deleted the one they already own?

You, sir, are a fucking disgrace. You embody everything the public finds repellent about the "arrogant techie" stereotype, and are unethical, deceitful and (if any money or reward changes hands as a result of your "service") likely comitting fraud to boot.

"All these users are older people who use their computers for web browsing and printing mostly, and I take my experiences so far as a kind of scientific 'evidence' that this class of users can't tell the difference."

So that makes it alright? Supposing one of them goes and buys a new family-tree plotting app, or garden-design program (to choose two examples my aunty recently bought) - what happens then? They're faced with a long, expensive call to tech support, which likely still won't the problem that you caused them. Eventually they (stupidly) turn to you again, and what do you tell them?

"Oh, right, yeah, that won't work - get your money back from the shop, if you can get them to believe that a version of 'Windows' won't run this certified 'Windows' application. Oh, and (if you're exceptionally lucky) here's a barely-maintained buggy-as-fuck butt-ugly hobby OSS version of something so pathetically niche that it'll never attract any kind of decent development community, to replace the version you just spent half your pension buying."

"If you service machines for friends and family try this. Don't ask, just do what is good for them. After all they are putting their absolute trust in your computer knowledge, to do anything less is to fail them in."

More like: "After all, they are putting their absolute trust in your computer knowledge, so to do this is to utterly and arrogantly violate that trust in the worst way possible."

Look, if you're sick of fixing computers for family, friends or others, just fucking tell them. Give them a choice of either switching to (your special version of) Linux or compensating you for the time you waste fixing their Windows boxes.

Alternatively, they can stop coming to you altogether and instead pay to have a computer shop fix it.

Under no circumstances is it ever ethical to violate their trust, especially not because you think you've got away with it so far.

For comparison, suppose you went to the doctor, and he told you you had gangrene. You'd expect some explanation of the options and some (pretty strong) recommendations, but ultimately it's your decision what happens.

You wouldn't expect the doctor to simply club you unconscious, chainsaw off your leg and bandage the stump.

"So what?" he might say - I've prevented it spreading to the rest of your system and killing you! You'll retain the use of your other limbs, and for anything you can't do with them, here's a half-arsed prosthetic replacement for your missing limb. Sure it might look a bit nasty, and doesn't always work too well, and sometimes breaks, but look - you can take the cover off and mess about with how it works inside! Ok, you're not a prosthetics expert, and so probably never will, but this clearly makes up for my complete lack of consultation before my arbitrarily rearranging your entire physiology!"

Jesus. Whatever happened to professional ethics?

You're the kind of person that gives us geeks a bad name.

Did someone named "DysenteryInTheRanks" just criticize someone named "ScuttleMonkey" for not being dignified, and is somehow surprised that someone threw poo at his head? :0