https://malpedia.caad.fkie.fraunhofer.de/ – The primary goal of Malpedia is to provide a resource for rapid identification and actionable context when investigating malware
https://talosintelligence.com – Talos Threat Source is a regular intelligence update from Cisco Talos, highlighting the biggest threats each week and other security news.
https://www.virustotal.com/gui – Analyze suspicious files and URLs to detect types of malware, automatically share them with the security community
https://www.eicar.org/?page_id=3950 – If you are active in the anti-virus research field, then you will regularly receive requests for virus samples. Some requests are easy to deal with: they come from fellow-researchers whom you know well, and whom you trust. Using strong encryption, you can send them what they have asked for by almost any medium (including across the Internet) without any real risk.