They do make this very clear on their site, but only at the very bottom of the download page and only on a page that is linked as "How does Viper use my essay?":
Aside from that, 9 months after your scan, we will automatically add it to our student database and it will be published on one of our study sites to allow other students to use it as an example of how to write a good essay.Right.
We tested the system in 2010 a the HTW Berlin, where it not only came in last as far as effectiveness goes, but we also observed that there was an essay mill at the same street address and with a telephone number just one number on from the Viper number. We called and tried to obtain more information, but the number only gave us an email address to contact, and our emails there were returned as undeliverable. We also observed that the email address that was used for the system was now getting regular emails like this:
I suppose we should be happy that they are at least publicly stating what it is that they do with the papers submitted. As Bailey points out, however, they also encourage universities to use the system, but since teachers do not hold the copyright to papers written by their students, they must violate the terms of service in order to use the system. What a tangled mess ...