Vsftpd is an FTP server, or daemon. The "vs" stands for Very Secure.
Obviously this is not a guarantee, but the entire codebase was written
with security in mind, and carefully designed to be resilient to
attack.

Recent evidence suggests that vsftpd is also extremely fast (and this
is before any explicit performance tuning!). In tests against wu-ftpd,
vsftpd was always faster, supporting over twice as many users in some
tests.