BT Openworld users were on the warpath yesterday, claiming to have been hit by a virus mailed out from the internet service provider's billing department over the weekend.

A number of readers contacted vnunet.com and started up a discussion thread on ADSLguide.org.uk, where it emerged that emails appearing to originate from BT Openworld's billing address were infected with the BadTrans Windows virus.

The virus appeared to be mailing itself to users who had sent emails to billing@btopenworld.com in the past few months. Emails intercepted by MessageLabs' antivirus scanning service confirmed that the email headers were from BTOpenworld.com.

BadTrans is a mass mailing virus and also drops a Trojan onto any machines it infects. It was discovered back in April and is protected against by most antivirus software.

Users received the emails on Friday, and then in increasing numbers over the weekend. BT Openworld managed to fix the problem and vnunet.com has received no new reports.

BT Openworld spokesman Tony Henderson said that the possibility of infection "hadn't been drawn to our attention previously". But he assured us that the company would be "running system checks" to track down the culprit.

One affected user said: "I got one too. Tried to open it (doh) but Zone alarm wouldn't let me, luckily. Maybe [BT Openworld's] billing department should have an up-to-date virus scanner and not run a mail program like Outlook."

Another user, who claims to have got an answer from the technical support desk, added: "I've just spoken to BTOpenworld and they have confirmed that a virus has been sent out and they claimed that the problem was now fixed. I explained that the problem may be fixed at their end but there are potentially 100s of users who's PCs are not fixed ... they did not offer any advice and just said sorry!!! Not very good!"

The user discussion thread can be found here.