Speak to your union rep as soon as possible if you have one. Also check what is in your company's electric communications policy, and any other relevant policies (e.g. anti-discrimination policies). If your company doesn’t have one, or if your offence isn’t mentioned in it, you may be able to successfully show that you did not know that you were acting wrongly.
If the policy mentions 'unacceptable', 'inappropriate', or 'offensive' material, but doesn't define more closely what that constitutes, you may also be able to show that you were unaware of precisely what activities were not permissable.
However, claiming that you were not aware of the policy will not be a defence if your company has advised you of its existence, or published it in an openly available staff handbook. You may well have to attend a disciplinary hearing.
Contact your workplace union rep if you have one, as they can accompany you in a hearing, and help you to put your case.
Of course, if you were using the Web in a way which breaks the law, for example fraud, or inciting racial hatred, then no excuse is likely to help you, and you may also face criminal proceedings, just as you would if you had done this from any other connection.
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