With the addition, the number of blocked files edges close to a hundred.
In order to thwart attempts by threat actors to sneak in malware inside certain files, Microsoft is appending ISO files, along with a couple of others, to the list of file types that won't be allowed to land in the inbox of Microsoft Exchange users.
ISO files are increasingly emerging as a popular enclosure for circulating malicious files and documents. Cybersecurity experts have warned that while Windows 10 can mount ISO files without relying on third-party tools, its contents aren't usually scanned by the operating system.
In fact, in a recent attack, threat actors relied on this behavior to pass compromised versions of documents that escaped Microsoft Office's Protected View protections just because they were rolled inside ISO files.
To prevent such attacks, Microsoft has tweaked the default policies of Microsoft Exchange to make sure that all emails with ISO file attachments are now automatically quarantined, giving users some pause to approach them more cautiously.