HI Laurène,
Looking at global stats every website is attacked 6000 times every single year, of course some sites are attacked more often, stronger.
In last update we improved security, but we always recommended to install additional firewall component + add security rules for .htaccess - that may reduce problem.
If possible ask hosting support to:
- Enable mod_security
- Lock/block all IP from Russia.
It will help a lot as well.
In general, security topic is very extensive, too long to even briefly discuss it here on the forum.