Tinder is for dating. Facebook is for friends. LinkedIn is for ... well, it depends whom you ask.

The professional networking platform is meant for connecting with colleagues, clients, and prospective bosses, but behaviour on the site can be far from the diplomacy of a boardroom.

In a lawsuit filed this week in Los Angeles, a mid-level financial industry professional identified only as Jane Doe alleged a recruitment conversation on LinkedIn took a turn for the inappropriate when she received sexual messages from a banker using his corporate account who had been trying to recruit her.

One of the messages included a photograph of his genitals.

Women have long complained of unsavoury conduct on LinkedIn, but in the California state court complaint, Doe argues that an employer is responsible for employee behaviour on the platform.

LinkedIn is an extension of the workplace, similar to going into the office or attending a corporate networking event, the theory of the case goes. If you wouldn't flirt on a conference call, don't do it on LinkedIn. If you do, you and your company could pay the price.

Between December 2015 and March of this year, Doe, who works for a Fortune 500 company in California, and Aaron Eichler, identified in the complaint as a managing director at SunTrust Robinson Humphrey Inc., a unit of SunTrust Banks, exchanged several dozen messages.

The two met when Doe, at a previous employer, worked on a deal that involved Eichler's company, Doe said in an interview.

Eichler initially messaged Doe about potential job opportunities. When Doe expressed interest in hearing more, the messages shifted from professional to not, she alleged.

"So what are you doing up so late?! Here's my number if you wanna play," wrote Eichler, according to court filings. He later added that it could be a "late night secret" before sending a graphic photograph, she alleged.

After Doe didn't reply, he wrote "Ugh, I guess I screwed up :( bummer dude."

The lawsuit seeks unspecified damages for sexual harassment, intentional infliction of emotional distress, and negligent retention and supervision.

"We take allegations of this nature very seriously, do not condone harassing conduct and take appropriate actions as warranted," a spokesman for SunTrust said before the lawsuit was filed. "Once we were made aware of the allegations we began an investigation that is ongoing."

"HR guidelines dictate that you don't sexually harass people at work - and I considered LinkedIn a work environment."

'Fair share of weird messages'

LinkedIn encourages members to report harassment by flagging conversations as "inappropriate or offensive." The company said it investigates incidents and takes "appropriate action," which can include being barred from the platform. In addition to reporting them, members can also block harassers.

Eichler still has an active profile on LinkedIn. In a telephone interview, Doe said she was shocked after receiving the photo, but didn't know how to block him on the LinkedIn app. Eichler didn't immediately return requests for comment.

Suzi Owen, a  LinkedIn spokeswoman, said sexual messaging like that described in the complaint "is prohibited and violates our user agreement, and we investigate and take action when violations are identified."

Despite billing itself as a professional network, unprofessional behaviour isn't a new complaint by users of LinkedIn.

"I've had my fair share of weird messages on LinkedIn, so my standard practice is not to accept invites from anyone (mostly men) that I do not know or are not affiliated with my industry," said a woman who works for a technology firm and requested anonymity for professional reasons. "In short, [LinkedIn] is not much more professional than any other social network site, in that people are messy and bring their messes everywhere."

Working on LinkedIn

LinkedIn is the closest thing Stephanie McDonald has to a workplace. McDonald, a South Carolina-based recruiter, runs her own business and spends the majority of her day messaging potential hires on the professional networking service.

She said multiple prospective candidates have asked her out on a date over LinkedIn, and she often gets flirty messages. Once a man asked if she would be willing to have phone conversations with him weekly for money. "That one was definitely the worst and made me think about getting off of LinkedIn," McDonald, 49, said.

McDonald sometimes responds saying she's not interested, stressing that she uses LinkedIn for professional purposes. "Some people don't say anything, some people come back and are pretty cruel," she said. She disconnected from a man who asked to pay for her phone companionship, but could still see when he would look at her profile.

If people want to transition a working relationship to a personal relationship, she advises they move to a different medium.

Hallie Crawford, a certified career coach, strongly advises against flirting on LinkedIn. "I don't think its appropriate, honestly, at all," she said. "It is supposed to be a professional platform."

No place for flirting

If people want to transition a working relationship to a personal relationship, she advises they move to a different medium. She tells clients to ignore any flirty messages. If the behaviour continues, she suggests reiterating the professional nature of the platform and relationship.

Occasionally, women are driven to delete their LinkedIn accounts entirely. Jennifer Hoffman, who identifies herself as a businesswoman and a former contestant on the television show The Apprentice, said she was asked on dates, hit on, and sexually harassed on a daily basis via the platform.

"I think that a woman with a public profile on any social media platform is subject to a certain level of harassment, but basic HR guidelines dictate that you don't sexually harass people at work - and I considered LinkedIn a work environment," she said. "So I deleted my profile. I don't plan on making a new one or joining LinkedIn again."

As for whether LinkedIn truly is an extension of the workplace - a place where under settled law an employer can be held responsible for the actions of an employee in the course of their duties - will be the subject of Los Angeles litigation.

SunTrust was notified of Eichler's alleged behaviour in a letter sent by Doe's attorney last month. According to the complaint, the financial institution's lawyer told her attorneys that "she was 'perplexed' why the SunTrust corporate defendants would be responsible for conduct committed by defendant Eichler using his professional LinkedIn account" and said his alleged behaviour, which included job recruiting discussions, was "outside the course and scope of his employment."

SunTrust didn't reply to a request for comment on the matter or the lawsuit.

'Insulting to say the least'

"Corporate sexual harassment training must meet the demands of an evolving digital world," said Doe's attorney, Ben Meiselas of Geragos & Geragos.

Doe, who said she received the lewd image on the same day she became engaged, has locked down her social media accounts.

"It's already hard enough being a female in this sector. To be treated as such after working so hard is diminishing," she said. "It's insulting to say the least.

"I fear, if I bring forward this complaint, it could very well be construed as a limiting factor in what I do for a living. At the same time, if I sit quietly, it eats away at me."

Bloomberg