A reader has kindly drawn to the IPKat's attention to a 7-page document from the European Patent Office, published in the Official Journal EPO 8/9 2009 (click here for full text): it's the EPO's notice concerning internet citations.
"3.1 Establishing the publication dateOf even greater interest to the IPKat, being a blogger, is what the EPO says about blogs as prior art:
Establishing a publication date has two aspects. It must be assessed separately
whether a given date is indicated correctly and whether the content in question was indeed made available to the public as of that date.
The nature of the internet can make it difficult to establish the actual date on which information was made available to the public: for instance, not all web pages mention when they were published. Also, websites are easily updated yet most do not provide any archive of previously displayed material, nor do they display records which enable members of the public – including examiners – to establish precisely what was published and when.
Neither restricting access to a limited circle of people (e.g. by password protection), nor requiring payment for access (analogous to purchasing a book or subscribing to a journal) prevent a web page from forming part of the state of the art. It is sufficient if the web page is in principle available without any bar of confidentiality.
Finally, it is theoretically possible to manipulate the date and content of an internet disclosure (as it is with traditional documents). However, in view of the sheer size and redundancy of the content available on the internet, it is considered very unlikely that an internet disclosure discovered by an examiner has been manipulated. Consequently, unless there are specific indications to the contrary, the date will be accepted as being correct".
"3.3.3 Non-traditional publicationsOn the whole, this seems a sensible approach to the problem, though the Kat reminds readers that the posting date and time shown on blogs created on Blogger is -- unless amended by the author -- are those that pertain to the opening of the file on which the post is created and not the time of posting. This post bears the time 11.28am, though it is actually posted at 12.04pm.
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 will 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".