A Swiss insurance worker was fired in April after surfing Facebook while off work sick. The woman claimed she could not work in front of a computer because she needed to lie in the dark.

Her employer, Nationale Suisse, said the action had destroyed its trust in the employee, reported news.com.au. "This abuse of trust, rather than the activity on Facebook, led to the ending of the work contract," it said.

The unnamed woman claimed her employer had been spying on her by sending a mysterious friend request to obtain access to personal online activity. But Nationale Suisse denied the allegations and said the activity had been stumbled across by a colleague, before the company implemented a ban and blocked the site.

2. Don't fake a sick day and announce it on Facebook

Sydney telco AAPT denied the incident, but in October 2008 correspondence between an employee and his boss made the email rounds. Kyle Doyle, a call centre worker, was asked to provide a medical certificate verifying a day of sick leave.

Doyle argued he was not required to produce a medical certificate for one day's leave, as stipulated in his contract. His boss responded that the company had determined that the leave could not be attributed to medical reasons, reported the Sydney Morning Herald.

"My leave was due to medical reasons, so you cannot deny leave based on a line manager's discretion, with no proof, please process leave as requested," Doyle responded.

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A screen grab of Doyle's Facebook page was sent, with the status update "Kyle Doyle is not going to work, f--- it, I'm still trashed. SICKIE WOO!," on the day in question.

Doyle's response? "HAHAHA LMAO [laughing my ass off] epic fail. No worries man."

3. Don't contact old workmates when you've been fired from the firm

Sacked lawyer Michael Mitchell from Clayton Utz sent a Facebook message to the human resources manager asking for her address in order to serve documents, because he was making a claim of discrimination.

But national human resources partner at the firm, Joe Catanzariti, wrote to Mitchell informing him that his online activities and tone of message were "cause for concern", reported The Sydney Morning Herald.

"It is reasonable to draw an inference that you have engaged in similar searches for other Clayton Utz staff with whom you are apparently aggrieved," he wrote. "Clayton Utz ... will not countenance any stalking, harassment or intimidation of its staff ... Affected individuals may want to take independent legal and other steps to protect themselves."

Mitchell, who has failed in attempts to bring harassment, discrimination and victimisation claims against former colleagues, including Catanzariti, denied he had done anything illegal and said the threats constituted bullying.

4. Don't criticise your place of employment or clients on Facebook

In November 2008, Virgin Atlantic sacked 13 cabin staff after remarks were posted on Facebook criticising the airline and some of its passengers.

The comments included insulting passengers by referring to them as "chavs" - a British term similar in meaning to Australia's "bogan" - saying planes were full of cockroaches and expressing concerns about planes flying from London's Gatwick airport, reported the Sydney Morning Herald.

Virgin Atlantic said in a statement that the staff had broken policies "due to totally inappropriate behaviour" and could not be expected to uphold standards of customer service.

"Following a thorough investigation, it was found that all 13 staff participated in a discussion on the networking site Facebook, which brought the company into disrepute and insulted some of our passengers," the statement said.

"There is a time and a place for Facebook. But there is no justification for it to be used as a sounding board for staff of any company to criticise the very passengers who ultimately pay their salaries," a spokesman added.

5. Don't post photos of your boss on Facebook

Back in June 2008, Prime Minister Kevin Rudd requested that his office and household staff remove their Facebook profiles after the publication of pictures in a newspaper.

Rudd's executive assistant, John Fisher, posted pictures from an overseas trip on the site which embarrassed the PM by showing party pictures from the 17-day trip to the US.

>> Read Part Two of 'Facebook No-No's'