How vulnerable is facebook ?

Is facebook a vulnerability ?
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During an orientation session in a company a IT guy was presiding about infosec and got on to say facebook is a vulnerability and thus it is a threat and .........

Is facebook a vulnerability ?
Facebook may be a huge futzing factor, but not necessarily a vulnerability, rather not a vulnerability.

Among the possible scenarios discussed were about people posting on facebook wall.
But employee of the company were not restricted from using facebook but facebook was blocked in office.

I suppose it was a clear case of accusing facebook to be a vulnerability.