Recently we've seen increasing reports of Cyptolocker style ransomware* being delivered in the form of RTF (Rich Text Format) attachments in emails. The RTF files attached are actually just Word docs with the file extension changed, abusing macros to run their code.
Unfortunately it seems that this particular brand of malware is avoiding detection by a large number of Anti-Virus/Anti-Spam tools currently. The usual advice stands, users should be highly suspicious of emails from unknown sources and not open any attachments they contain.
As RTF files aren't commonly used for legitimate documents nowadays our recommendation for most businesses would be to block them at their mail server or spam filter. If you'd like any further advice on protecting your business from malware please get in touch, contact details can be found here.
*Ransomware is a nasty type of malware which attempts to encrypt all your data and force you to pay for the decryption key. Once you've been hit often the only choice is to restore the data from a backup or pay up for the key.