It's a website where people can ask one another questions. And if they opt for anonymity, they can do so without ever being traced.
Ask.fm site has about 60 million users worldwide; about half are under the age of 18.
The attraction to teens: On Ask.fm, millions of youths talk about their hookups, struggles and wild weekends, with no adults to peer over their shoulders.
But some also use the site to anonymously torment other teens. With its popularity soaring, Ask.fm is coming under attack from parents, politicians and privacy watchdog groups.
This week, the site announced changes to prevent bullying, including making it easier to report inappropriate behavior and allowing users to opt out of receiving anonymous communications.
Also, certain features of the site will no longer be available to those who don't register with an e-mail address.
Ask.fm is based in Latvia in northern Europe and most of its activity is abroad. Already five suicides in Britain have been linked to the website.