To be clear, there does not appear to have been any malware created that utilises this exploit, though some have already jumped the gun and said that malware exists and it is threatening thousands of Windows computers.
However the researchers claim that the exploit is publicly available (exploitdb and Metasploit); it has already been used in the wild in a limited way; and Microsoft have stated their intention not to patch 2003 servers.
They did not offer any evidence of the exploit being used in the wild. It would need a malicious payload to be attached in order to make anything like the impact which WannaCry did.
According to Secarma, Web Distributed Authoring and Versioning allows users to move or copy files, documents or pages on a Web server or web share.
ExplodingCan uses a buffer overflow in the PROPFIND function of WebDav; by sending a long request the condition is triggered and any given payload may then be executed.
Secarma checked online and found 375,000 servers on the Internet running this version of IIS, but said that not all would be vulnerable as only those which had WebDav enabled were susceptible to an attack.
The company said it used the publicly available exploit module from the Metasploit project and found that it worked and yielded a shell on a Windows server in the lab.
They then tested it by converting it to Python code which would allow them to tag on a payload of their choice.
But they then realised that testing servers on the Internet to find out which were vulnerable - and which folders on these machines had WebDav turned on - would be against the law.
Hence they contacted the UK National Cyber Security Centre and handed over the research they had done.
Microsoft has ended its support for IIS 6.0 and thus is not issuing any patches for it.