Hidden networks

Are you talking about wi-fi networks? Hidden wi-fi networks are those which don't 'broadcast' their name. When you search for networks you will usually see a number of your neighbours' networks, but any which are hiding the name - which may include yours - don't show. However you can use the option to enter the name and password manually. There is no difference otherwise in the connection.

Cellular (mobile) networks don't hide their names - there wouldn't be any point.

The password will always be hidden (otherwise there would be no point in having it). Not broadcasting the name simply means other people can't see it (though an experienced hacker would have no problem) so it provides a small extra level of security. The main security is your password, so make it something strong (not 'password' or 'fido', and certainly not the default your router came with).

I wouldn't until you get that resolved. You could be on anything.