Tattoodle, an app for creating and sharing virtual tattoos, and posting them on your profile, has gotten as popular as real tattoos over the summer. It grew from 891,000 monthly active users three months ago to 2.76 million a month ago and 4.24 million today. It added 104,000 new users just yesterday and 542,000 in the last week.

The basic idea is not new, so it’s interesting to see this app growing. The brightly-colored and widely divergent styles virtual types tattoos may have a special allure. The app lets you choose from categories of tattoos like “animals,” “creepy,” “man’s ruin,” “nautical,” and “skulls.”

The developer behind the app is called, interestingly, Make The Web Better. The company site says that it makes its money from a browser toolbar called Fast Browser Search. “It is through revenues generated by search that our Company is able to offer and continually enhance our world-class products free-of-charge,” the site says. While using the app, it is easy to navigate to a web page that also offers virtual tattoos but cleverly disguises a “Make Tattoodle my homepage” option into the background of the page. As the site explains, you first click through to add your tattoos (and maybe make Tattoo your homepage), then you’ll see its Fast Browser Search bar installed.

So, it appears Tattoodle is heavily monetizing through toolbars – a practice which can be lucrative, but has been historically criticized for overly aggressive advertising practices.