Some Facebook group sites provide a venue for users to vent their frustrations about scamming. (Photo by Zach Schonbrun/CNS)

Andy Hall is tall and slim, always has been, and his secret to staying slender does not come from a pill.

So when he woke up recently to see messages from far-away friends asking him about the possible benefits of a weight-loss supplement, Hall, 25, was momentarily confused.

Then he checked his Facebook wall.

It seems that the night before, Hall had inadvertently clicked a faulty link that scattered posts advertising a new “weight-loss pill as seen on Oprah” to all 503 of his friends, many of whom he has little or no connection with currently. It left him feeling a bit embarrassed, and worried about what other dangerous weak spots may be hidden on his Facebook wall.

“I probably would never click on an ad or a link again just to be safe,” said Hall, a commercial appraiser in Washington, D.C. There are many scams that “people don’t know about that could get people pretty upset, I’m sure.”

Five years after Facebook opened its site to the public, scams have been an unfortunate side effect for many of its 500 million users, luring people to phony sites or links and often gathering valuable personal information. But in some cases, scams that send unwarranted messages to an entire friends list can feel like an even worse violation.

These messages run from the innocuous — “Click here for a free iPad” — to humiliating — “I’m on a new male enhancement pill, check it out” — to even hurtful, like what happened to Philip Gysemans, who had the names of several friends posted on dozens of Facebook walls in response to a quiz question about his sexual experiences.

“Several of my friends noticed the response and a few of them were offended by the result,” said Gysemans, a warehouse worker in Belgium.

With typical friends’ lists growing to include coworkers, family members, religious leaders, even bosses, the personal ramifications of unknowingly transmitting an embarrassing Facebook message can often be overlooked.

And the number of Facebook scams seems to be on the rise. A January report by Sophos Security, a United Kingdom-based antivirus firm, showed that more than double the amount of those polled reported both spam and phishing targeting in the last two years, and nearly double said they had been sent some form of malware.

For its part, Facebook successfully sued Sanford Wallace, the self-proclaimed “Spam King,” for more than $700 million in October 2009, and its own security page is liked by more than 3.7 million people. The page offers near-daily tips and updates about how users can protect their profiles.

In its privacy policy, Facebook says: “We are not responsible for third party circumvention of any privacy settings or security measures on Facebook.”

An e-mail message to Facebook’s press relations department for comment on its privacy was not returned.

After a scamming episode in 2008, Griffin Hammond, 26, set up a discussion page called “Facebook Phishing Scam Awareness” where followers can post their own lessons in dealing with scams or vent their frustrations. When he launched it, Hammond believes it was the only security group out there. Now there are more than 5,600 members.

“I set up the page mostly to let all of my friends know, who were maybe going to be victimized by a common friend, what they need to do and what to avoid,” said Hammond, a video editor for State Farm Insurance Company in Bloomington, Ill. “Pretty quickly the page got a lot of followings because a lot of people are dealing with this stuff.”

While technological scams have been around for years, managing a personal online profile — and the importance of keeping up that reputation — is a relatively new social phenomenon. But scams can take away that sense of control. Even if an embarrassing episode does occur, an apologetic mass message cannot always cover it up entirely.

And some scams are getting tougher to recognize. That vulnerability has rubbed off on many Facebook users who are growing increasingly wary about a site they used to enjoy freely.

Nineteen-year-old Shelby Sadler of Whately, Mass., was upset when she found out she had posted a message on her friends’ walls about a “picture of them they need to check out,” followed by a faulty link. What bothered her most was she had no idea what had prompted the scam attack.

“I was super embarrassed because it posted on people’s walls that I didn’t ever really talk to,” Sadler wrote in an e-mail, adding that she “felt violated that the Facebook advertisers had taken it upon themselves to use my Facebook as free advertising space.”

“The biggest implication is that people need to be educated about the privacy issues and risks of new technologies,” said Dr. Pamela Rutledge, director of the Media Psychology Research Center, a nonprofit organization that studies social media and culture. “For most people, there will be tedious steps to take to set things right.”

Those unused to the pitfalls of new technology — new users or especially older generations — are typically more susceptible to being scammed. Like Bill Chastain, 53, who accidentally clicked a link he saw posted on someone’s wall that sent a message about “creepy Facebook profiles” across his friends’ list.

“I didn’t even know I did anything wrong,” said Chastain, a sportswriter in Tampa, Fla. “I was embarrassed about it and I put up a message that said ‘Oops, didn’t mean to do that.’ I was just hoping it would go to my close friends, not everybody.”

Rutledge is hopeful that as more information is passed around about the prevalence of scams, the more users will become aware and also accepting of a shameful quiz result made public. The scams will not disappear; the vulnerability might.

“Embarrassing things will always happen,” Rutledge said. “But to me, it would be more important to arm people with tools and understanding to increase their savvy and psych resilience.”