See if your online accounts have been compromised
https://haveibeenpwned.com

https://sec.hpi.de/ilc/

See if your password has been used before
https://haveibeenpwned.com/Passwords

Test your website security
https://www.ssllabs.com/ssltest/index.html

Test your email security
https://www.checktls.com

Report phishing and malware
https://decentsecurity.com/#/malware-web-and-phishing-investigation/

Report a UK data breach
https://ico.org.uk/for-organisations/report-a-breach/

National Cyber Security Centre
https://www.ncsc.gov.uk

Cyber Essentials
https://www.cyberessentials.ncsc.gov.uk

Critical Security Controls
https://www.cisecurity.org/controls/

Decent security for everyone
https://decentsecurity.com

Secure web development
https://troyhunt.com

Secure web configuration
https://scotthelme.co.uk/

Open Web Application Security Project
https://www.owasp.org/index.php/Category:OWASP_Top_Ten_Project

Demystifying the Windows Firewall – Learn how to irritate attackers without crippling your network
https://channel9.msdn.com/Events/Ignite/New-Zealand-2016/M377

Standard test suite for your anti-virus software
https://www.amtso.org/security-features-check/