Anything you post on the Internet is there for eternity - even if you delete it, it is there and can be traced.
As a rule I tell all my staff NEVER post on the internet (or for that matter include in an email) anything that you would not post on a public billboard on the side of the highway.
Also it pays NOT to use your work computer for any personal internet access or email as corporate IT departments monitor usage, can capture and examine email you send, and are legally entitled to (at least in Australia). Generally you will have been made aware of the corporate policy on acceptable usage of email and internet when you were first employed. You may even have had to sign a document acknowledging that you have read and understood it.
Believe me, using the internet does NOT make you anonymous or immune to disciplinary action, or worst case scenario, dismissal and/or prosecution.