The Register reported that BT notified one of its four million retail broadband customers, who requested to remain anonymous, accusing her of illegally downloading a copyright song from an open source file sharing program.

The email included evidence gathered by the British Phonographic Industry - the trade association that represented the interests of British record companies, namely, combating copyright infringement.

The evidence shows records of the customer downloading Girls Aloud's "Biology" in May from Ares, which can be used as a client for both Gnutella and BitTorrent networks.

The BPI has formed partnerships with major ISPs like BT and Virgin Media to cut down on the number of infringing music copyright cases.

It is unknown whether BT has complied with the record industry's "three strikes" policy, which sends two warnings to those accused with infringing music copyright before suspending or disconnecting their account. Earlier this year, Virgin Media joined Tiscali to become the second major ISP to implement the three strikes system.

And while BT said it cannot comment on the cases of individual customers, a spokesman assured that all BT broadband customers who are engaged in similar copyright infringement practices will be met with the same threats of service disconnection if the BPI can supply the proper evidence.

In the case of the anonymous customer, the BPI provided comprehensive evidence against her consisting of the Ares user agent, a timestamp, a file name and an IP address.

To compile this evidence, BPI investigators can attain lists of IP numbers involved in copyright-infringing peer-to-peer networks and detect their ISP. If the ISP agrees, it can then single-out the exact account holder without revealing any personal information with the BPI.

And while hardcore downloaders are able to employ technical tactics to prevent detection, the record industry says it hopes to at least gain control over the mass market.

In the letter, a member from BT's "Customer Security Team" writes:

"I have received a complaint regarding one of our customers offering copyrighted material over the internet. On investigation, I have found that your account was used to make this offer. This activity must stop immediately. Sorry, but we're obliged to point out that further similar problems may have to lead to the termination of your account, as such activity contravenes BT's Acceptable Use Policy."

The email then tells the customer she should secure her Wi-Fi connection and delete all filesharing software from her computer, as well as relay the message to anyone else in the household. The full letter can be read here.

This incident represents further action by the record industry in fighting copyright infridgement involving online file sharing networks. Last month, a Connecticut man was jailed for 30 months for copyright infringement for his involvement with Warez sites.