The fake e-mail appears to have been sent from "email@example.com" and was first spotted on Friday evening with a subject line: "RedHat: Buffer Overflow in 'ls' and 'mkdir'".
The e-mail contains instructions on how to load and install a 'patch', which Red Hat warns is likely to contain malicious code.
Red Hat said its official security messages are sent from firstname.lastname@example.org and are digitally signed.
According to the company's Web site: "All official updates for Red Hat products are digitally signed and should not be installed unless they are correctly signed and the signature is verified".
Windows users have been successfully targeted a number of times with malware disguised as a fake 'security update'.
One of the most successful worms of 2003, Swen or Gibe.F, was disguised as a Microsoft patch to fix a flaw in Internet Explorer.
Less than four months later the tactic was tried again, but this time the Xombe or Trojan.Xombe worm, posed as a critical update for Windows XP.
The most recent attempt to fool Windows users was the Sober.D worm that masqueraded as a fix for the MyDoom worm.