It doesn't even take any depth. I've cited wikipedia on my website (the intent was to link to more information, not to utilize it as an exhaustive source) and later gone on to visit that link to make sure it still says what I want it to say only to find out that since I cited the article, the article cited the very page on which I had cited it. Whoever cited my page was either too lazy to check the bibliography, which was at the foot of the page as normal, or didn't care that they were potentially creating a circular reference one reference long.