They're probing for a backdoor in shell/log.php. Yours isn't compromised if your log.php matches what Magento 1's should be, but if it was compromised, that payload would presumably indicate to the scanner that your site is in fact vulnerable.
The parameters are all possible request keys that backdoors in log.php might look for. This is the shotgun or '...
The most important thing is to make sure your magento version is patched with all security updates.
Assuming that you magento has been installed correctly ( folders and files have the correct premissions etc), then there is other things you can do to be extra safe.
The biggest thread to being hacked (bar having a vulnerability due to out of date ...
I added the below code into my .htaccess file.
You can check with .htaccess file in the root path or in the Pub folder.
# Deny access to files with extensions .ini, .psd, .log, .sh
Deny from all
It helps me. Hope this will help others. :)
One easy solution is, if you are not using nginx, than rename nginx.conf file to 'nginx.conf.sample' in root directory of your magento installation.
This worked for me, and the warning message disappear in Magento Admin.