It looks like the https certificate on r-project.org is currently expired. I am sure sysadmin in Vienna is on it, but perhaps we can prevent this from happening again by adding a check in R or the mirror report [1] to warn about mirrors with https certs that are about to expire: library(openssl) certs <- download_ssl_cert("r-project.org") cert_verify(certs) # Error in cert_verify_cert(cert[[1]], cert[-1], root) : # Certificate validation failed: certificate has expired as.list(certs[[1]])$validity # [1] "Mar 10 17:14:13 2014 GMT" "Mar 10 17:14:13 2016 GMT" PS: the cert that is deployed on r-forge.r-project.org is valid for *.r-project.org and is valid until 2018 so that should make an easy fix: cert <- download_ssl_cert("r-forge.r-project.org") cert_verify(cert) as.list(cert[[1]]) [1] https://cran.rstudio.com/mirmon_report.html