iChecker

If you're a Yahoo Messenger user, you sure know that anyone who runs this application has the option to stay invisible, so that the others won't know if that user is online. Well, there are some tools that can turn that into a myth and iChecker strives to be one of them.
This tool is designed in order to help you find out whether a certain ID is connected to Yahoo Messenger or not, regardless if it's on the invisible mode or not.
Since it's such a simple application, iChecker is being delivered as a very light package, this means it that loads in a second on any computer. The interface is minimal so it all comes down to writing the ID belonging to the persons you wish to check if they are online and pressing the 'Check' button.
We've tested it with multiple IDs and we can confirm that iChecker doesn't always work as it should. For example, an ID is not flagged as being online unless the contact uses the dedicated 'Online' mode. In case they're on the invisible mode, iChecker marks the ID as being offline. Otherwise, the app remains very light on computer resources, so it works pretty easy without hampering the computer at all.
Among the available features offered by this utility, you have the possibility to add the Messenger ID to your Y!M list, send a message or a file and view the profile of that person.
Overall, it's safe to say that iChecker could use a better detection rate but it is still very useful for those who want to sign-up for a new account. With this tool they can check if a particular Yahoo! Messenger ID is available or not.