On Windows, when CPAN.pm has to fall back to using ftp.exe, it's possible for the failure to download to create an empty MIRRORED.BY file, which triggers a refetch, and repeats in an infinite loop.
Bug #17237 for CPAN:
This queue is for tickets about the CPAN CPAN distribution.
ANDK [...] cpan.org
adamk [...] cpan.org