(This is going to become the EndUserDocumentation?. Obviously just an idea collection currently.)
On newer Web sites and services, you may login with an user account/profile from a different site. This of course requires that you have an account on another site which provides this profile sharing service too.
If this is the case, then "username»profile±service" is the username that you can enter in the login forms on any new web service. Beware that such an user identifier can't be used as E-Mail address, even if it looks like one.
Note: The email-like syntax is not supported by most OpenID sites - you have to provide your identity "URL" to login there. Right click your user name on your login service page, and select "copy link address" to get it.
This section should list icons and explanations for:
Whenever you try to login, please first try to login with only your "username»example" name in the login box. Leave any given password field empty. Web sites that explicitly ask you to give out the password of your @profile-service.com account, could be malicious and trying to trick you.
There are however still many sites, which yet don't comply with the newer and safer password-less login systems (which are technically more complex). If a login fails, then this could be the case and you could then try it with also entering your password (or secondary password) from your login service providers site. You should however only do so, if you trust the new site to a certain extend.
Strangers could login with your name on other web sites, if they've set up a fake site which allows them to write down your password once you've hit submit. You may not even notice that someone steals your password.
With the newer login systems you don't need to type in a password for every service you'd like to use. You however still have a password on the site where your main user account/profile resides on.
If you login on other sites, you occasionally get redirected to a "remote login" or "user account sharing" page, where you again have to enter your accounts primary password. Here you should take care, that this is indeed your providers page by verifying the server name in your web browsers address bar. Criminals had set up similar-looking trick sites in the past, so you should take care that you don't get tricked here.
