http://spywareitdaiuyfo2sqb5vsg7mek5cjabdr73luhnda57t2hyuzg7yyd.onion/articles/paint.net.html
Paint.NET is self-updating software Paint.NET contains an updater that downloads new version of Paint.NET. This updater also downloads a file from paint.net's website to check for new versions, which is a form of phoning home.
(I didn't check what protocol or kind of request it makes, though) This can be disabled, however, and you should disable it.