Which sounds perfectly reasonable, but it's not necessarily the truth. As another commenter posted here, this has happened before with WoW users [1].

They claimed that they tried and failed to replicate the failure, but anyone who's done any kind of software development knows this is far from conclusive proof.

A post mortem on the logs of the banned accounts is absolutely necessary. If they're not willing to do that, they should at least refund the accounts.

[1] http://www.linuxlookup.com/2006/nov/22/blizzard_unbans_linux...