While traditional advertising still works quite well — especially television — there certainly are some big changes afoot. The fact is more people are spending their time on social networks like Facebook and Twitter. And the big brands — like Pepsi (NYSE:PEP), Kraft (NYSE:KFT) and Starbucks (NASDAQ:SBUX) — are getting aggressive with the medium.

But as is the case with any new frontier, there are landmines. One case is McDonald’s (NYSE:MCD), which recently got caught in a tweetjacking situation.

Huh?

So, McDonald’s promoted the hashtag #MeetTheFarmers to get real-life stories about the company’s trusted suppliers and their healthy ingredients. It was a smart idea and elicited some good tweets.

But then came the big blunder — McDonald’s introduced another hashtag, #McDStories. The problem? By including the McDonald’s brand, the hashtag became a target for a deluge of negative tweets. Here are some examples:

“#McDStories Take a McDonalds fry, let it sit for 6 months. It will not deteriorate or spoil like a normal potato. It will remain how it was”

“Watching a classmate projectile vomit his food all over the restaurant during a 6th grade trip. #McDStories”

“I once worked at McDonalds. I have never eaten there since. #McDStories”

Social media can be an incredibly powerful and positive marketing tool — but McDonald’s learned the hard way that it also has its risks.

— Tom Taulli, InvestorPlace.com