(This is possible, for example, when you download R using an unsecured Wi-Fi network.) This could potentially give an attacker the same rights you have to execute code on your system. If you download R (or R packages) using an unencrypted Internet connection, there is a possibility that a malicious actor could modify the code in transit (or substitute their own file), if they have access to the connection linking you and the CRAN server delivering the code.
These recommendations are not unique to R: you should follow similar practices for any software you download from the Internet.
The R Consortium was formed to serve the interests of the R user community, and to that end the members of the R Consortium would like to share some best practices for using R securely and safely.
