See https://www.virginmedia.com/help/security/malware-alert
https://community.virginmedia.com/t5/Security-matters/VM-Malware-letter/td-p/4766613
"If you have received one of these alerts, it means we believe a device in your home has been infected with malware that’s sending malicious traffic to other computer systems, and could be trying to access them without authorisation.
We realise this is unlikely to be your fault, but this kind of abuse is against our Acceptable Use Policy. If the abuse continues, we might have to suspend or cancel your broadband service. It is therefore important that you follow the advice provided."