I thought it was more or less required to defend your trademark, else you could loose it.

He also needs to have registered it in the first place. Trademarks are not automatic like copyright is.

I didn't try very hard, but I couldn't find a "curl" trademark here for software:

http://tmsearch.uspto.gov/bin/gate.exe?f=tess&state=4808:iz1...

Sort of. The USA you can claim trademark rights without a registered trademark; that's the difference between ™ and ®.

But the law follows "use it or lose it" rules. If you don't defend your trademark, then in the eyes of the court it is no longer a trademark.

Hold on, that's "defend it or lose it". Author of libcurl clearly is using the name, there are new releases coming out quite often.

My wording was unclear, yes. If you aren't defending it, you aren't using it as a trademark.

Think of the term literally; if it's not exclusive to you, it's not longer a "mark" of your specific "trade". It's just a "mark".

Fair enough.

>He also needs to have registered it in the first place.

Not true. Unregistered marks can still be defended (it's just harder).

That's why there's both ™ and ® symbols. Trademark and Registered Trademark.

That's true. But he's allowed to choose to lose it, or to discuss with Google and grant a trademark license.