Because of the POODLE attack it is recommended to disable SSLv3 (eg see https://disablessl3.com/ ). Disabling it in the client and server means that a MiTM cannot force to downgrade the connection to a vulnerable protocol.

However, QSsl::SslProtocol currently only has the option to force a specific TlsV1_x. This is too specific. It would be useful to have a protocol QSsl::AnyTls, or even better, a bit field to disable or enable specific protocols. Something to inject SSL_OP_NO_SSLv3|SSL_OP_NO_SSLv2 at the OpenSSL level.