The firm said that preliminary analysis - following notification early on Monday - revealed that a malicious PDF file can be distributed in the form of an email attachment which drops and executes when opened on a fully patched system with either Adobe Acrobat or Reader installed.

The rate of infection is extremely limited, however, and as a result, Symantec's risk assessment of the security vulnerability is low.

Symantec, which said that the file has been identified as Trojan.Pidief.H, recommend that internet users ensure their anti-virus definitions are up-to-date and not to open any files sent from a suspicious source.

A spokesperson for Adobe said that the security vulnerability has been confirmed and that an update - and patch - will be released as appropriate.