Privacy Control can warn users when sending confidential information.

It also warns users if they are using an unencrypted wireless network.

While the on-line services have repeatedly warned users not to fall for such schemes, some nonetheless did - and still do.

Privacy rights advocates warn users about uses for the information that can be gathered through social media.

That, at least, can warn users of a pending problem.

But they do have a call alert that warns other users you are trying to reach them, a feature sure to annoy your children.

The site's homepage now warns users the service is "unavailable indefinitely".

They didn't warn users that this change was coming, or get their approval in advance.

This warns users that the product may contain bugs, and could be unfit for general use.

Trading sites like americandreamcars.com, puppydogweb.com and equine.com have warned users about the scheme.