Can software be immoral? That depends, i have to say no actually. The original intent, purpose, or theory of the software can be evil based on the creator, but it is the user of the said software that determines what it does and how it does it.
For example, lets use your hammer example.
Creator one makes a hammer, and states "This is a tool to build homes". He sells the hammer to a local carpenter, who proceeds to bash in his wifes skull.
Creator two makes a hammer, and states "This hammer is to be used to kill". He sells the hammer to a local sadist, who proceeds to build a house for a group of less fortunate children.
In both situations the tool was created and used for two different purposes. The tool is a inanimate object that has no control over anything that happens to it, and its use and purpose was entirely defined on the user.
So was the hammer evil? No. Was the one creator, and one user evil? Absolutely.