The internet is also used to exchange and publish information in ways which did not exist before, via, for example, Usenet discussion groups, blogs, e-mail archives of mailing lists or wiki pages. Documents obtained from such sources also constitute prior art, although it may be more involved to establish their publication date, and their reliability may vary.
Computer-generated timestamps (usually seen, for example, on blogs, Usenet or the version history available from wiki pages) can be considered as reliable publication dates. While such dates could have been generated by an imprecise computer clock, this should be weighed against the fact that in general many internet services rely on accurate timing and will often stop functioning if time and date are incorrect. In the absence of indications to the contrary, the frequently used "last modified" date can be treated as the publication date.