https://www.proofpoint.com/us/resources/e-books/ransomware-survival-guide
This guide from proofpoint provides information on what to do before, during and after a ransomware attack. I also provides comprehensive guidance on how to break the attack chain and stop ransomware attacks
https://www.shsu.edu/intranet/policies/information_technology_policies/documents/IT-24%20Malicious%20Code%20(v1.02).pdf
This sample policy from Sam Houston State University is an example of a policy to reduce risk by protecting against malware.
https://www.sans.org/white-papers/68/
This SANS whitepaper discusses several common practices which, when implemented together, will greatly decrease, and perhaps almost stop malware.
https://help.ubuntu.com/community/Antivirus
The official Ubuntu website provides open source and proprietary antivirus options that support Ubuntu and other flavors of Linux.