The alleged founder was arrested
The alleged founder, Artem Vaulin, was arrested by the US government inside Poland. This move led to the shutting down of the site.
The US seized the domain names
The US authorities seized the domain names associated with the site, thus preventing it from coming online.
One of the servers was located in Chicago
The reason the US government was able to charge Artem Vaulin is that one of his site’s servers was located in Chicago.
Copyright infringements charges
The founder is facing charges of copyright infringement, as the website allowed people to illegally download software and files that are protected by copyright laws.
Distributing $1 billion of copyrighted materials
The founder was charged for distributing well over $1 billion of copyrighted materials. (See Why is Groupon failing?)
Confusing copyright claim process
The site uses a lengthily and confusing copyright claim process to prevent people from completing the process to the end and so keeping the copyrighted material on the site.
It had some of the big copyrighted titles
The site had some of the big copyrighted Hollywood titles, and as a result, it got more attention, which eventually led to the lawsuit. (See Why did Radioshack fail?)