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David O'Callaghan writes:
: Once an invention has been made public it cannot be patented by : another, so it would be impossible for a company to 'steal' open : source material.
I think this is intended to mean that it is "impossible" for a company to patent an idea that has been published as open source software. Except I can think of at least one case where this has happened: Network Associates' broad anti-spam patent which was applied for in December 2002 and comes way after SpamAssassin and also after Paul Graham's article on Bayesian Spam filtering from August 2002 (http://paulgraham.com/spam.html).
Actually, that patent isn't such a good example -- it's not as broad as it was presumed to be by many. (I can't go into too much detail here though, for various reasons.)
A more recent case is TitanKey's patent on per-user whitelisting and blacklisting of email messages performed during the SMTP transaction, which had prior art in the open-source Obtuse SMTPD, among others. See recent ASRG mailing list traffic if you're curious. That one is extremely broad, and with clear prior art, I've heard.
I cannot talk too much about patents in the anti-spam field, as I generally avoid reading them due to the idiocies of software patents in the US.
- --j.