How can we detect that Ollydbg is used to debug an application
You know that message boxs that tell us to close Olly before we continue
I hate it!!!

And something else, is it possible olly can't attach to an active process?
I am getting an error msg "unable to attach to process"

_http://pe-lib.sourceforge.net/pumqara/html/code_protection/Detecting% 20OllyDbg/DetectOllyDbg+Pum.htm

_http://pumqara.cjb.net/

That's good,thank you
Do you know any other ways to do that?

Search yourself for a book "Crackproof Your Software" (author Pavol Cerven) . There are some other tricks.

Allmost informations in "CrackProof.." book and of Pumqara is old, and can be bypass by some anti-anti-debugger plugins.

Crack PROOF? Well there's a misleading title if ever i've heard one. From what ive read on Amazon it seems like a good book to help newbie programmers stop their programs being modified by newbie crackers, but that's about it.