This is what i think of as a problem of the study of the whole and its parts. In the form of a system that transmits information via packets, the internet must be a medium. In the form of the screen that the user sees, it is a series of mediated documents and hypermedia, or more and more frequently just lexia wrapped in figurative images that compose mutagenic documents that are experienced as individuals. The internet does have sources in though, some are fixed. The key idea for a source... it seems to me is it's authority, which is usually associated its provenance. So even in today's climate, paper derived documents seem to be preferred to fixed form digital originals, which are usually preferred to mutable texts. So is the internet comprised of sources? yes, but they are not always the same kind of sources, and some people might not consider them sources at all, depending on how they view sources. The information that is transmitted does come from somewhere though, that is true. However, the information that is received might only be a permutation of the original. so the answer is 'yes' it is a source and medium depending on definition.