The general availability phase for .sx, a country code domain name for Sint Maarten, begins today.

Already a number of large web sites have protected themselves by defensively registering equivalent .sx domain names — a domain that looks awfully close to .sex.

I just checked the top 30 web sites in Quantcast to see if they were registered by their respective brand owners. This is easier said than done, since whois.sx has been giving server errors for the past half hour.

Among the companies that have registered .sx domains are Google, Yahoo, Microsoft, and Tumblr.

It appears that most Mark Monitor clients have taken the opportunity to defensively register .sx domain names.

Google’s registrations include google.sx, youtube.sx, blogger.sx, and blogspot.sx.

Facebook and Twitter, haven’t protected their brands in .sx yet.