Actually, the letter contents were toned down from the following,

Dear users,

We had a breach in our systems and it wasn't prevented as soon as we could as our staffs were busy setting up the new rates for RMAH and explaining to the Board of Directors how money kept flowing in automatically. Sad but true, your accounts are compromised and while we kept ourselves busy counting figures that kept flowing in, it's up to you to safeguard your account.

kkthanksbye,
Mike