If you're a frequent Facebook user you know all about those "free" ads that pop up on your timeline — postings that offer two free Air Canada tickets, a $100 Ikea gift certificate or free pizzas, to mention just a few.

The problem is, they're not real. The offers, shared countless times by unsuspecting Facebook users, illegally use well-known company names and logos.

Calgary resident Arthene Riggs saw the so-called Air Canada offer after it was shared by her sister, who received it from one of her friends.

"I thought, 'Oh, my sister sent it. I should be good. Let me just try it and from then it's been a nightmare,"' Riggs said.

Her account was subsequently shut down by Facebook, which sent a message saying the offer was spam. She had to open a new account with a different name, losing all her contacts, before Facebook subsequently gave her instructions to restore her original account.

A look at Facebook feeds shows Riggs is not alone. Many have shared an offer for a $100 Ikea coupon, which was also a scam. It was shared widely in Nova Scotia, where Ikea is opening a much-anticipated store this month.

"Please be aware this is not an Ikea website or a website affiliated to Ikea and the offer is not authorized by Ikea," a company spokesperson told CBC News.

This fake offer is one of many making the rounds on Facebook. (Facebook)

But aside from losing your Facebook account, what is the danger of liking, sharing or answering questions on fake offers?

Ed McHugh, a marketing expert at Nova Scotia Community College, said in some cases the fake offers are intended to infect your device with a virus or worm. In other cases, it's hackers out to see how many people they can fool.

The problem, he said, is sharing or liking the offers "can lead us down a rabbit hole to anywhere on the planet."

"You don't know what kind of villains or viruses you're opening yourself up to, which could destroy the technology you have, or maybe even be phish that could take down the technology and phones of friends," he said.

Air Canada and Pizza Hut

The Air Canada offer has been around for almost two years. On Sept. 23, 2015, Air Canada posted this message on its Facebook site: "There is currently a scam on Facebook that claims to offer two free Air Canada tickets. To protect your personal information, do not respond, share with your friends or 'like' the post."

In response to the most recent fake coupon, Air Canada spokesperson Isabelle Arthur said the company has posted a warning on its website.

She pointed out Air Canada isn't the only airline affected by this scam and said it has contacted Facebook and the hosting provider of the website to shut it down.

Last year, Pizza Hut was targeted and posted a message on its Facebook page warning customers there was a "fraudulent coupon circulating on Facebook claiming to offer a free pizza from Pizza Hut." It characterized the post as "a scam."

CBC Nova Scotia's Consumer Watchdog shares some ways to protect yourself from coupon scamps. 1:16

McHugh said such offers are hard to resist.

"One of the most Googled words is 'free,'" he said. "The word is quite intriguing to many, many people and they get pulled in."

McHugh said the offers are giving the scammers what they want, otherwise they would stop.

"If you were to talk to online investigators or police, I suspect they only hear about 20 to 25 per cent of this stuff, so who knows how big the number is?" he said. "I think a lot of people who actually get suckered in by these offers don't even report it."

How do you know?

Facebook said its members who click on spam may be unwittingly installing malicious software or giving people access to Facebook accounts, which are then used to send out more spam.

Facebook's website said it has "dedicated teams across the company that focus on protecting people."

The company also said it's built tools to prevent and remove spam. It urges users to report spam to Facebook so it can protect others.

So how do you know what's real and what isn't?