According to this email, which is currently hitting inboxes around the world, the recipient has been invited to a "Free Meal Day" courtesy of fast food giant McDonald's. The message claims that all one needs to do to get the free meal is print of an official invitation contained in an attached file and present it to any McDonald's store on 26 June, 2011. There are several variations of the emails, some of which refer to a "Free Breakfast Day" rather than a "Free Meal Day". Subject lines and listed menu items also vary.
The emails are certainly not from McDonald's and the offer of a free meal is entirely bogus. In fact, opening the attachment that comes with the emails can install malware on your computer. The attachment contains a .zip file that in turn harbours a malicious .exe file. Launching the .exe file installs a Trojan horse that connects to third party websites and downloads and installs further malware components.
If you receive one of these emails, do not open any attachments or follow any links that it may contain. Malware distributors regularly use similar tactics to trick people into infecting their computers. Users should always use caution when opening attachments or following links in unsolicited emails.