A marketing campaign by O2 that sent customers USB-embedded pens backfired last week – after it transpired a number of devices contained a "Windows-specific virus."

The UK cellphone network sent out the USB pens to its business customers followed by a marketing email encouraging them to download a free eBook. That was then followed by another email warning that the USB drive inside the pen contained malware.

The email titled "Urgent: Information about potential virus" warned that some of the promotional USB embedded pens had a Windows-specific virus, that "may not be picked up by out-of-date Anti-Virus software."

The message, seen by The Register, warned that for anyone using their computer as a web server, the virus would also attack anyone who visits their website.

"The virus has the ability to install new programs onto your system including updated versions of itself and programs that might grant the virus’s author remote control over your computer."

The mobile network said the majority of the USBs were not infected and blamed the gaffe on a supplier issue, adding it had "notified the relevant organisations."

"If you have already and your antivirus has flagged a risk, please follow the instructions your antivirus software gives you and then remove and dispose of the USB," said the email.

The virus infects program files and web files on computers running the following systems: Windows 2000, Windows 95, Windows 98, Windows ME, Windows NT,Windows Server 2003, Windows Vista, Windows XP.

An O2 spokesman said the business had contacted all customers who received the USB and advised them to discard it.

He said: "For any customers that have already used the USB or are concerned, we have a specialist team on hand to support them and guide them through any action they may need to take. We apologise for any inconvenience." ®