Programs, scripts, disk images and, optionally, Android apps are blocked by extension. A second extension in front of it (invoice.pdf.exe) and right-to-left tricks that show a harmless ending are blocked as well. Defendr also reads the first 64 KB of an attachment, so a program renamed to cute-cat.png is still caught. Archives sent with a password hint are flagged, because a scanner cannot look inside them. There is no virus scanning.
Example
/setup › Find a setting › Android apps