We think it might be. We have asked through our private Superuser's Forum what is happening. You are not the only one that has noticed this.
Superuser 2017/18 Use Kudos to say thanks Mark answer as "helpful" only when the problem is solved Please don't send me private messages unless I ask you to. I do not work for VM. The advice I give is based on my best understanding of VM policy and practice. You rely on it at your own risk.
To be honest this influx of spam is not entirely unexpected. Your default webmail spam settings were set to 'reject all spam', which resulted in VM customers reporting non-delivery of expected mail and non-VM companies being reporting being unable to send mail to VM domains.
So we've altered the default spam setting to 'deliver spam to spam folder'. The previous setting allowed you no initial control over what happened to your spam whilst our most recent update empowers you to make you own choice.
Please click on the links below for more information about this: