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How did my contacts suddenly end up on iCloud when I didn't give permission to do such? Where is your security and privacy commitment for your own software, Apple? No wonder celebrities get hacked. They hack 1, and then you get a list of phone numbers and emails for a whole bunch of other A-listers.
These are the Developer Forums, where developers of apps for Apple's platforms ask each other for hints and tips on coding.
Your question is more of a product support one, so I'd suggest you ask future questions over at the Apple Support Forums.
On this occasion, though, I'll help you out...
Are you using a Mac, iPhone or iPad?
It's pretty much the same journey on all devices:
You can disable that if you want, but somewhere along the way you enabled it when you signed into iCloud.