>> No, it is a violation of company policy
That is the rule. Working for a defense contractor, my employer uses the phrasing of "mischarging" when canning you.
But I voted for:
>> Yes, but only on breaks
Simply because the term abuse is best applied. Stories of firing usually involve casual internet use of about 4 hours a day. So, as long as you don't abuse it, you are fine. I use the net maybe 15 minutes a day for personal use. Most days 5-10 minutes. If they fire me over that, so be it. I wouldn't work for them anymore if that's there concern in life.