In England, if you can show that such an ad impairs the system, it violates the Computer Misuse Act, which prohibits non-consensual use of computer services to harm users.
You'd have to show actual harm, but this is Microsoft. Actual harm is quite possible. Being the OS owner would not exempt Microsoft from the provisions of the Act.
The same will apply to their forcible upgrades.
The relevant part is section 3. Section 3 of the Computer Misuse Act makes it illegal to perform an unauthorised act with intent to impair, or with recklessness as to impairing, the operation of a computer.
In both the above cases, recklessness applies.
Section 3A of the Computer Misuse Act makes it illegal to create, supply or obtain any article for use in committing another offence under the Computer Misuse Act. Article includes software.
Non-blockable ads and imposed updates constitute creating tools for reckless interference, whether or not the tools actually cause damage.
The example on the police.uk website is this:
You downloaded a programme which was able to take remote control of a friend’s computer without their knowledge. You didn’t get a chance to use it before you were caught. This offence covers the possession of ‘malware’ but also legitimate software for which you had the intent of using it to commit an offence.
In this example, we can see that intent to use is sufficient.
Section 3ZA of the Computer Misuse Act makes it illegal to perform an unauthorised act causing, or creating the risk of, serious damage of a material kind. If the damage is caused or threatened to human welfare or national security you can go to prison for life, otherwise the maximum sentence is 14 years in prison.
We know from Heartbleed and from the effects of ransomware that ICU computers on the Internet use Windows. If these crash, due to a non-blockable popup or a forced upgrade, there's material damage. We only need to show there's a risk of it, we don't need to show it actually happening.
Clearly there's a risk. That puts Microsoft in violation of 3ZA.
The act is here: https://www.cps.gov.uk/legal-g...
IANAL, but I can see that a common reading of the Act puts the popups and forced updates in violation. Ownership of the OS is not considered an exemption anywhere in the text. The text clearly refers to the computer and the users thereof, not the owners of what is running on it.
A lawyer would be needed to say if the forced popups or the forced upgrades actually broke the law. Actually, I suspect it would take a court case, so there's case law on the subject. This is because legal uses of a word don't always match common uses.
But I'd contend that there is a reasonable expectation that the law would cover such cases.