Are you required to claim ownership of the site?

Not sure how many people here will want to help your cause. Sounds like you're looking to do something illegal.

Look at the case of Pirate Bay in Sweden... shady websites with no clear owners. Even in court, they keep pretending that they have no clue who "owns" or "controls" the website.

So do you have to say who you are? No. But as soon as significant money comes your way, it will become an issue. If all you have on your site is a blog talking about your cat, no one cares.

Are you required to claim ownership of the site by your company in the footer or the about page?

No, in most cases you are not required to do so. Some countries have laws that mandate this, fx. in Germany a "impressum" may be required. You should see a lawyer in your area for a more precise answer.

Common wisdom in the micro-ISV community is that you have to earn trust before a sale, and this involves being completely transparent about who you are. If you don't your sales will suffer dramatically.

And if not, how does anyone else can legally find out if the site is owned by you personally or your company.(taxes/lawsuits etc)

Very easy, look up the domain ownership in WHOIS. All DNS records are public and show ownership information. Additionally, if you're selling something, follow the money trail to the recipients bank account -- most credit card issuers and banks will happily tell who owns a merchant account.

You are not anonymous on the Internet, certainly not when people bother to actually investigate things. Domain ownership is registered, your web host will most likely have logs of administrative access to your website, these logs have IP addresses registered, IP addresses can generally be followed to a household ADSL / cable modem, and so forth.

Its kind of like evidence that the police gather at a crime scene. Treat IP as evidence and establish a clear chain of custody. You may want to sell the business, enforce a copyright or defend against a disgruntled designer.

Since its rather easy to do .. well :)

The whole 'user interface' thing was settled years ago. What remains is copyright, trademark and (gasp) software patents. I'm guessing you have neither.

While domain and site ownership are far from the same thing, I suspect most courts would consider them synonymous. If it's not clear who the owner of the site is then likely the owner of the domain for the site would be good evidence of ownership of the site itself. Though obviously, IANAL.

I also share @Ian's unease with this question... Unknown guy form yahoo, your integrity is your most important asset in this game.

It's good business practice to state who you are on the web - especially if you are going to be asking people for money for your product. Re taxes - that depends on what your selling, where.

Bottom line, if you're going to be legit, state who you are.