[dudul]

Yes. If you use company provided resources to create Foo, Foo belongs to the company. Same if you do it during company time, or while in the office.

Plus, depending on your state law, they may own stuff you do on your spare time if you don't have a document listing projects that belong to you.

Edit: I'm not a lawyer, rules depend on state law, you should ask one specialized in your state of residence.