Emails are coming in to email accounts around the world that are exact duplicates of emails received months, or even years ago.
There is one significant difference from the original: a virus-infected Microsoft Office file is attached.
Someone has managed to get access to email archives from multiple email providers, and is using these to send incredibly legitimate-looking emails to users, to distribute their virus.
This virus is currently poorly detected by antivirus software; as of this writing, 31/60 on virustotal.com.
Until more is known about this virus, it's best to avoid opening any Microsoft Office file attachments received by email.