If the employer is worried for security reasons, they can send the employee home but must pay his salary for 3 months (in France at least, I don't know for other EU countries).

The same assumptions are made in the EU, the only difference is that the employee is let go, but still continues to receive his salary for some months.

Think of it more like a severance package and it makes more sense.

This is supposed to protect both the employee and the employer.

The employee to give him some time to find a new job (he is entitled to some days off during these 3 months to interview).

The employer to (at least theoretically) force the employee to still work to prepare a handover, docs, etc.

What happens in practice depends on the case : these 3 months may be shortened via a mutual agreement, the employer may force the employee not to come to work (but still pay him) and other arrangements are possible.