If you've been dismissing the ever-insistent Windows 10 update pop-up by clicking the "x" in the top right corner, be careful. Microsoft has employed a classic malware technique to trick you into installing the upgrade -- the "x" now means you're happy to begin installation.
Previously, the pop-ups didn't have an "opt out" option. You could "Upgrade now" or "Start download, upgrade later". So of course, clicking on the "x" has become second nature.
Now there is an option to "Click here to change the upgrade schedule or cancel scheduled upgrade". If you have accidentally clicked on the "x", the install can be declined during the installation process.
If you've already gone ahead, and want things back the way they were, you can use the 30-day rollback feature from the Recovery Menu in Windows 10.
This tactic comes after Microsoft announced it would be ending the free Windows 10 updgrades on 31 June, with the software to be priced at $199.
Some great news from that announcement was that the constant pop ups would be ending altogether, with the "Get Windows 10" app that facilitates the easy upgrade to Windows 10 disabled and eventually removed from PCs worldwide. But it seems Microsoft are trying to get the most out of them while it still can.