Beckhoff Embedded PC images before 2014-10-22 and Automation Device Specification (ADS) TwinCAT components do not restrict the number of authentication attempts, which makes it easier for remote attackers to obtain access via a brute-force attack.
https://www.cisa.gov/news-events/ics-advisories/icsa-16-278-02
https://ics-cert.us-cert.gov/advisories/ICSA-16-278-02
https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2016/icsa-16-278-02.json
https://download.beckhoff.com/download/document/product-security/Advisories/advisory-2014-003.pdf
https://download.beckhoff.com/download/document/product-security/Advisories/advisory-2014-002.pdf
https://download.beckhoff.com/download/document/product-security/Advisories/advisory-2014-001.pdf