Posting a joke or a gripe on Facebook can now be hazardous to your career.

The popular social networking site as well as other forms of social media from blogs to instant messaging are blurring the lines between work and personal matters. And that means it has become a concern for bosses and employees.

Earlier this month, newspapers here reported a case where a male teacher resigned because his Facebook profile contained links to pornographic websites.

Cyber security expert David Freer from Symantec cautions: "What goes online stays online. Even if it has been made public for only seconds."

It is best to always think twice before hitting 'enter', say experts. Especially since local recruitment agencies estimate that up to 20 per cent of companies may look up a potential employee's online profile.

Tay Kok Choon, a spokesman for recruitment agency JobStreet Singapore, says: "Employers don't mean to pry into people's private lives but, rather, to get an idea of their personality. For example, will an individual behave very differently after a few beers? Uploaded photos may provide some clues."

But how far is too far when it comes to posting personal material online? And what about innocent water-cooler speak, from the boss' newest hairstyle to gripes about that annoying colleague?

Among more than 20 companies from various fields surveyed by LifeStyle, few have specific guidelines for staff on online conduct, while most declined to comment.

Bosses and HR consultants generally feel that the onus still lies on the individual. But no guidelines does not mean no consequences.

Student J.X. Tan, who is in his 20s and worked for an advertising firm, blogged about his work details and complained about a boss.

He was given a verbal warning by senior management and asked to take down his entry.

Tan says: "Ever since then, I've limited access to my blog and Facebook profile. When friends post comments or bitch about certain lecturers at school on my Facebook page, I delete them."

A teacher, who wants to be known only as Jane, says that she also restricts her Facebook profile.

The site has settings where users allow access to only verified friends who have to be 'added' manually.

Jane adds: "I never add my students. I tell them I will add them after they graduate. My colleagues create a separate Facebook account that their students can access while keeping their personal ones secret."

Executive director of the Singapore Human Resources Institute David Ang says: "Most company guidelines will state that staff cannot post anything defamatory, portray the company in a bad light, or disclose sensitive business information. But this is done in a broad sense.

"Even if you have specific guidelines in place, there comes the question of policing. How are you going to enforce it? The Internet is so pervasive that not everything can be controlled."

Some companies overseas, however, do try. The BBC has specific online principles published on its website for staff.

The company states that where staff can be identified under its name, they "should not use the Internet in any way to attack or abuse colleagues".

Danny Loong, creative director of food, beverage and live music chain Timbre, says he has official policies where employees are told that they "should not post online comments about the work they are doing or the workplace".

"We're dealing with a different generation of workers. So bosses have to recognise these issues."

At the end of the day, it is always good to play it safe like management executive Lorraine Lai, a former Miss Singapore Universe finalist. She says she was always careful about what she posted on her blog while taking part in the 2005 pageant.

The 24-year-old sums it up: "If you have the guts to put things up, you better be prepared to face the consequences."