McAfee claims to have uncovered a spear phishing campaign in which hackers are exploiting Microsoft Word to access confidential data at a French firm.
Yahoo France and La Poste email accounts are said to be used to send out malware to monitor networks, with hackers possibly impersonating the firm's employees, according to the security firm.
Chintan Shah, security research lead at McAfee, said: "Spear phishing email is a major worry to any organisation.
"Messages that appear legitimate and specific fool us more often than random phishing attempts."
The payload of the attack appears as a seemingly innocent word document, with the email message pretending the attachment is a legitimate part of company business.
Once the malware has been installed it logs the communication of the temporary file directory, collecting information about the network and connections of the company, in what Shah describes as "spear phishing reconnaissance".
The domain names connected to the campaign have previously been flagged for distributing PittyTiger malware that exploited vulnerabilities in Microsoft Office against telecoms, defence companies and governments.
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