At one point, the phrase “in the cloud” probably meant something useful and specific. These days, though, it has just become a buzzy marketing term for “the Internet.” “Your files are safely stored in the cloud!” “You can send video messages through the cloud!” “You can order books from the cloud!”

You mean the Internet? Oh.

Internet services such as these have become essential elements in the Apple, Google and Microsoft ecosystems. Have an iPhone? Then you have a big incentive to get a Mac and an iPad, too—because Apple's free iCloud service will make sure that your calendar, address book, e-mail, to-do list, notes and passwords are magically synced with all your Apple gadgets.

Have an Android phone? You'll want to stick with Google's Web browser, tablets and laptops for the same reason. Microsoft, too, has automatic syncing among Windows computers and phones and the Web.

If you take the bait and marry into one company's ecosystem, great! You enjoy astonishing convenience—free. And if this “in the cloud” stuff makes you a little nervous, no problem! You can opt out and confine your data's location to your own zip code.

At least that's the way it used to be.

Lately, the big tech companies have been quietly removing the option for you to keep your data to yourself.

Here's a startling example: Did you know that you can no longer sync your computer's calendar or address book with your Apple phone or tablet over a cable? Starting with this year's version of the Mac operating system, Mavericks, you can sync them only wirelessly—and only through an iCloud account.

Something similar is going on with Microsoft. In Windows 8 and 8.1, you can log on to your PC with either a local account (your name and password are stored on the PC) or a Microsoft account (they're online, like in iCloud). A Microsoft account automatically syncs your familiar settings, bookmarks, and Facebook and Twitter account information with any Windows 8 computer you use.

But Microsoft tries hard to make you feel like a loser if you choose the local account. (“Not recommended,” the screen tells you ominously.) Many features aren't available or convenient without a Microsoft account: your SkyDrive, your photographs, the built-in Music app—in fact, you can't download any apps from the Windows store.

Online accounts are handy, but they're also imperfect. If you have an iPhone 3G, you can't connect to iCloud. If you're traveling out of Internet range, no syncing can take place.

There's an economic issue, too. The more data you're shuttling to and from the cloud, the faster you eat up your monthly Internet service allotment.

These cloud services keep your personal information perpetually backed up—another plus. Yet your hard drive isn't the only one that can die. From time to time, those big online services go down, too—Gmail has gone dark, Amazon services have crashed—and at that point, you can't get to your own stuff.

Above all, there's fear. You're no longer in possession of your own data. You're making them available, at least in theory, to Apple, or Google, or Microsoft. Or the National Security Agency. Or to a hacker. All it takes is one teenager, somewhere—anywhere—guessing your Hotmail password, and suddenly you're locked out of your own PC.

The big computer companies are quietly, slowly forcing us to entrust our life's data to them. That's a scary and dangerous development.

In fact, it may be that “in the cloud” really isn't the best term for the services these companies offer. What they really want is to have us “on the leash.”