As we've covered here before, private servers are a violation of license limitations of the EULA. Blizzard considers any violation of those license limitations to be copyright infringement and sues people for such. Furthermore, Blizzard established in the "Bnetd" case that crafting software to set up a private server is a copyright infringement all on its own.
The total reward of $88,594,589 comes from $3,053,339 of inappropriate profits, $63,600 of attorney's fees, and $85,478,600 of statutory damages. Statutory damages are damages required by law that are increased for willful and commercially based infringement. Scapegaming may appeal the amount.