In New York State there are three basic classes of employee:

1. Hourly employee: If you show up at work, punch a clock, and are paid overtime, then you are an hourly employee. Factory workers are commonly hourly employees. As an hourly employee the company owns the hours you are at work, and has no other claim on you. I believe it is uncommon for programmers to be hourly employees.
2. Contract worker: In this case you are working per defined contracts. The work you do on that contract is (barring specific contract provisions saying otherwise) owned by the company that has hired you. They have no claim on your time or energy when you are not working on the contract. Many programmers work this way. But if you are (for instance) hired by a consulting company to work at clients, then your employment with that consulting company is not contract work, see the next option.
3. Professional employee: This is the rest of us. Professional employees have employment that is not defined by a clock or by a contract. In fact under the law their productive output belongs to their employer, 24x7, 365 days a year (366 on leap years). It is customary for these terms to also be spelled out in employment contracts very clearly, though truth be told most people read these, sign them, and have never given the contents of those contracts much in the way of thought.

This brings me to intellectual property law. Intellectual property law in general assigns the rights to intellectual property to the creator of an idea, work, or implementation. That creator gains delimited control of their creation. In theory the reason for this is to encourage potential creators to create new things, and for them to pass into the public domain. Or at least this was the reasoning that Thomas Jefferson used (and he got it from French thought on copyrights), though the reality in this century has not matched theory very well.

But who is the creator?

One would think that the creator of a work is the author, the person who actually produces it. But the realities of life are not so simple. What if one person conceives of an idea, and then gets multiple people to implement it? Is it owned by the implementers, or the person who thought it possible and paid for it to be done?

The legal resolution is the doctrine of a work for hire. A work for hire is a work that you produced for someone else, and they own all rights to any potential intellectual property that might arise from that work. (Including, obviously, both copyrights and patents.)

Now what happens if you combine these two legal areas?

The answer is unambiguous both in theory and practice. All work covered under your employment terms belongs to your employer. In the case of professional employees, this is everything. If you go home and write something on the weekend, you do not own it. You might be unaware of this issue and naively put a copyright notice on it, then distribute it. That was your mistake.

Now let me make this personal.

I am a professional employee. I signed a routine employment contract while I was still pretty much of a novice as both a programmer and an employee. As is common, 6 months later I had completely forgotten about the terms of the contract and was blissfully unaware of the laws I live under.

My bad.

Over the course of this job I have slowly become more and more involved in open source work. I write software for fun and release it. I have put code into posts here, released stuff on CPAN, and even contributed a core perl module. All of which I thought I had the right to do, but as it turns out none of which I did. There isn't even a legal issue to contest, I simply didn't know better.

My very bad.

As of today here is the status. This came up from an incidental issue about a month ago. I have been told that if I wish to continue being employed, I cannot post code. If I continue being employed, then I will be admonished for the code I have released so far. If I leave my employment then the decision about what happens with any and all of the code of mine that people here have seen is not mine. (Stupid comment removed.)

I live in NYC. It seems likely that my wife is going to have no option about moving any significant distance for at least a year. I am carefully considering my employment options. I have a likely job prospect near Philadelphia which would allow me to work on open source stuff. That is farther than I want to commute, and the pay cut would be painful, plus it does not resolve the other issues. I have not seriously searched for any potential jobs which are closer.

Now my food for thought for everyone is this. How many more people are in the same position I am, and are not aware of it? How much open source software has been put out there by authors who thought they owned rights that they do not? If you are an employee, are you one of them?

These are, as I have just learned, extremely non-hypothetical questions.

UPDATE
There is, considering the circumstances, only one choice for me to make which is not abysmally moronic. Do not expect to hear much from me in the future.