Domain name hijack?

Hey all, probably not the best place to ask this but thought that I would give it a shot.

At my company I manage 30 or so domain names through various registrars, they existed before I came on board. Today I received an email from a person claiming ownership of one of our valuable ones, valuable to us anyway since we have an ASP product sitting behind it. Whois database says that is clearly belongs to him and the ICANN registrar is not one that is being used here, last updated 6 months ago. If this would have been changed 6 months ago I would have been the one to change it, and I didn't change anything.

    Created on..............: 2001-May-20.
    Expires on..............: 2010-May-20.
    Record last updated on..: 2005-Jul-25 21:29:10.

The domain is still pointing to our DNS servers, we haven't had any outages to this point, looks like the admin and tech contacts were the only thing changed, and now 6 months later they want the domain.

I've got calls into the current registrar to see what is going on, they were contacted at the same time I was and need some time to see what's going on. Anyone have any advice? Should I call ICANN? How can I find out what that change was on July 25th?

Are they in .org? If so, I would call PIR. More generally, I would suggest you contact the registrar, not ICANN.