Nearly all software with any creativity is automatically copyrighted from the moment it is created. That's the law and nobody can change that (at least not soon).
However, it is up to the copyright owner to decide if and how these statutory rights are going to be enforced. Some people give away these rights freely in what is called "free software". They have simply decided it is more valuable to them that people use the software than it is for them to make a profit. Such software generally has no strings attached, other than perhaps acknowledgment that you got it from someone else (screen credit).
Open source, on the other hand, is a different license that may have other constraints. For example, you may be allowed to use the software for personal use for free (without paying royalties on the copyright), but you cannot use it to make a profit unless you agree to share the profit (or to at least credit the open source as the font of your success). Also you may be allowed to have access to the source code and make modifications (derivative works, which is another exclusive right of the copyright owner), but you have to agree to SHARE those changes with everyone else as the price of being allowed to use the modified software. This is a big problem for companies that believe they can use "open source" as the basis for a commercial product, modify it, keep the modifications secret and thus profit by filling a market need that others cannot. Unfortunately for them, this is a violation of the open source license and they can be effectively sued in federal court for copyright infringement and have to divulge the trade secrets that were incorporated into the open source product.