Cyber-attacks become less effective when they are well-known, so new threats and exploits appear all the time. To keep up to date, you should monitor websites and newsgroups.
Some examples of threat intelligence feed providers and sources for threat reports, alerts, and newsletters include:

• Alien Vault (https://www.alienvault.com/solutions/threat-intelligence)
• SecureWorks (https://www.secureworks.com/capabilities/counter-threat-unit)
• FireEye (https://www.fireeye.com/solutions/cyber-threat-intelligence-subscriptions.html)
• Symantec (http://symantec.com/security-intelligence)
• Microsoft (https://www.microsoft.com/en-us/wdsi)
• DarkReading (https://www.darkreading.com)
• SANS (https://www.sans.org/newsletters)