Are you sure the BT email account was hacked?
It is quite possible the spammer just got a list of email addresses and spoofed them. This can be done very easily and requires no access to the account itself.
EDIT to add: Just thought that as you received the email from the friend it is likely their address book is compromised. However, it is just as likely that this is via a virus/malware on their own PC harvesting the address book rather than the BT account itself.
Edited by ian72 (Tue 27-May-14 13:22:42)