[Nessa]

There used to many program that had the ability to do this but with changes made a few months ago, these programs have become very unreliable. They will more often that not, give you false positives, which in my opinion isn't even worth the try! There are other ways people can try to check if you are invisible like inviting you to a conference but all you have to do is log out and you'll avoid having to respond at all!