Standard practice when hiring any employee is to write a legal agreement stating that any work you do there is "work for hire" and they own the copyright, not you. I *think* this can even be implied just by the fact that you were an employee, Unless you took specific action before writing this code, such as giving the company a specific license, or requireing them to let you contribute it, I think you are the one in *possible* legal danger here. (I am not a lawyer etc blah blah).
This is unfortunate but you need to get over the fact that work-for-hire does not belong to you and drop this quickly. The more you drum up publicity around this the more danger you could be in.
Chalk it up to a learning experience, and take solace in that you know what to do next time.
At the last company I worked with I asked my boss (a SVP level executive good enough for legal purposes) to sign a small contract with me that would allow me to bring in my own open source libraries I had built up over the years in exchange for letting me take code written on company time and contribute it back to the library or to an OSS project. I of course said this would not include anything proprietary to a client or any program as a whole, but rather utilities such as a date converter class or caching system. And that it was at my sole discretion to determine as best I could in good faith what code qualified to be contributed to open source.