How can I hide whois information?

Most domain registries require whois information to be publicly available, at least where the domain name is used commercially. The exact rules will depend on the TLD of the domain, and possibly who it was registered with.

Another option is to use on of the "private registration" services that will set themselves up as the owner/contact in whois, and will act as an intemediary for any communications, giving you effective privacy.

I don't know of any way to retroactively hide yourself once you have put the information out there.

I registered domains through a registrar who automatically puts their own address in there for you instead of revealing your address. There are several registrars like this.

It is pretty easy to make up an address. I have personally left the wrong address in my personal domains and just kept one public email address correct.

I get a threatening letter that I must make it accurate, but how would they know, and I can say they really don't care.

It cut down on my junk snail mail for business services.