Online bulletin board Pinterest is blowing up. In fact, stats from comScore first obtained by TechCruch show that it could be one of the fastest growing Web sites of all time.

Launched in 2008, Pinterest last month hit 11.7 million unique monthly visitors in the U.S., crossing the 10 million mark faster than any other independent American site, comScore said. That's up from 418,000 when it was founded nine months ago and 7.5 million in December.

It's worth noting that Formspring founder Ade Olonoh pointed to data from Google Analytics that showed Formspring crossed 10 million global unique views in two months, but it's difficult to compare data from two different tracking firms, as they gather their data in completely different ways.

Pinterest's growth hasn't been driven by the typical early adopters from the East and West Coasts. Rather, the site has been boosted by women ages 18 to 34 from middle America. Pinterest's biggest user base comes from the Central Southeast and the Midwest, with a strong showing in states like Missouri, Kansas, Minnesota, and Mississippi, the data showed.

ComScore said on average, Pinterest users spend 98 minutes on the site each month. By comparison, Tumblr users spend an average of 2.5 hours and Facebook users spend an average of seven hours.

To put this growth into context, other sites that have generated comparably impressive traffic in a such a short amount of time are tied to other services, like Google's social network Google+.

Despite this report of astounding growth, there could be a controversy developing for Pinterest. LLsocial.com has claimed that the site is modifying pins without informing users.

LLsocial's Josh Davis explains: "if you post a pin to Pinterest, and it links to an ecommerce site that happens to have an affiliate program, Pinterest modifies the link to add their own affiliate tracking code. If someone clicks through the picture from Pinterest and makes a purchase, Pinterest gets paid. They don't have any disclosure of this link modification on their site."

Davis said this is notable because Pinterest is already monetizing while still in beta and because it's been so hush-hush about this activity.

Pinterest did not immediately respond to a request for comment.

For more on Pinterest, check out this infographic that shows the site is driving more traffic to retailers' Web sites than Google+.

Also see PCMag's full review of Pinterest and the slideshow below.