I don't know about France, but in the USA many publicly owned computers (which includes government agencies and state universities) are subject to a de minimis personal use standard. That is, you are allowed to use the publicly owned computer for personal use if it does not interfere with your work and is "minimal". If the use is brief, infrequent, of little or no cost to the state, and is not disruptive, then a “de minimis” use of state resources would not be unethical. Typically bandwidth is included in this concept. So, if you are at home using your own bandwidth (e.g. to listen to the internet radio or watch an internet movie), you are not really using much in terms of state resources. However, as soon as you start streaming these things from work, or storing those files long-term on your work computer, you have overstepped your ethical bounds.

Though, your employers should already have their own policy in place regarding personal use.

I don't know about France, but in the USA, some states have policies for publicly owned computers (which includes government agencies and state universities) and are subject to a de minimis personal use standard. That is, you are allowed to use the publicly owned computer for personal use if it does not interfere with your work and is "minimal". If the use is brief, infrequent, of little or no cost to the state, and is not disruptive, then a “de minimis” use of state resources would not be unethical. Typically bandwidth is included in this concept. So, if you are at home using your own bandwidth (e.g. to listen to the internet radio or watch an internet movie), you are not really using much in terms of state resources. However, as soon as you start streaming these things from work, or storing those files long-term on your work computer, you have overstepped your ethical bounds.

Though, your employers should already have their own policy in place regarding personal use.