Matt Bromiley, senior principal consultant with Mandiant, offers checklists for how small-to-medium businesses can identify and clear ProxyLogon Microsoft Exchange infections. The four vulnerabilities described in Microsoft s communications to date do not appear to affect Exchange Online or Office 365 services. If you have on-premises Exchange, or a cloud-based version of Exchange, the next step is to close off the vulnerabilities using the patches released by Microsoft is to patch your system as soon as possible.
Source: https://threatpost.com/mandiant-microsoft-exchange-exploits/165439/