"You've been Chosen to Win a $1,000 Walmart Gift Card! But only the 1st 1,000 users that enter code 7777 at <some bogus site> will Receive it!"
Probably just a scam to get malware on your computer/phone and get info on you. Because it has to be quite plausible that a company will just give away $1,000 for entering a four digit number, right? You do not even have to go to their own site, but some *.mobi site with a stupid name indicating no affiliation with Walmart.