Viruses on the site, redirect files, can't find the source?

Question

Malware

https://yadi.sk/d/Oc_hPtbz3GGiXU
There are 2 files with a virus code in the archive, I delete it in all sites, and it reappears in a day, and in 2 seconds it spreads to all the first folders of attachments.
How can you track it?

Answer 1

How can you track it?

Track - in the logs.
But "how to get rid of" is another question.