It is, if upon written request, the terms are confirmed by the one offering the bounty. This has happened here. The originally reporting newspaper has this to say (translation by me):

"[...] The doctor had noted the biologist's 100.000-Euro-Offer on the internet. At the start of the trial, he stated that he had requested (and received) written confirmation of the bet. He sent the documents to the biologist - together with his account number. Still, he did not receive the money and proceeded to sue. [...]"

Original article here: http://www.stuttgarter-nachrichten.de/inhalt.kurioser-masern...

Thank you, that makes it credible.

It's an offer, which can be accepted by someone complying with the terms. At that point it constitutes a contract.

http://www.bailii.org/ew/cases/EWCA/Civ/1892/1.html CARLILL v. CARBOLIC SMOKE BALL COMPANY; admittedly that's English law rather than German, but the principle holds. That case also deals with rewards, diseases and pseudoscience.

There also seem to be a number of U.S. cases enforcing unilateral reward offers as contracts; a theme seems to be that they intended to get other people to do work and those people reasonably relied on the offer and did the requested work (most often going out and finding a missing person or item).

I believe the doctrine is called Promissory Estoppel: http://en.wikipedia.org/wiki/Estoppel#Promissory_estoppel

Yeah, it looks like that's the theory.

In Germany, bounties are relatively strictly regulated by law in terms of what you may and may not do etc. Therefore, if the bounty itself was valid in the sense of the law, then - AFAIK - there's an obligation to pay up.

Absence of a legal contract for such cases exposes a website to abuse. I refuse to believe that a text posted publicly is subject to the same standards as a real contract.

As rostigerpudel stated, the biologist confirmed the bounty in writing.

Anyhow, while IANAL, bounties are regulated by German law in (among others) BGB §657-661a. Mostly §661 and §661a. You can find a translation of those paragraphs here: http://www.gesetze-im-internet.de/englisch_bgb/englisch_bgb....

Thanks for pointing those out. I never noticed them before.

Perhaps it is in Germany?