I have a software project which is essentially a heavily modified piece of open source software. I'm wanting to add copyright notices to the file headers to protect my work, as it is possible for users to extract the source code. Some files are totally original, some are modified, and some match the original open source project.
Can I put a "Copyright " notice on each file? If not, what about "Subject to copyright - contact for more information" - would it be as effective of protection? If I put a "Copyright " notice on a file I didn't edit, what are the potential consequences?