I successfully installed MathType 6.9 on Windows 7 Pro 64 bit, running Office 10, and NAV File Insight flags the install file "Many Users, Mature, Good". It works fine, no problem with many hours of use. When I tried to install the same on my Windows 8.1 64 bit laptop, NAV quarantined the install file. NAV File Insight (same version, multiple site license) on this computer flags the same install file "Many Users, Mature, BAD--many indicators this file is untrustworthy". Repeated these NAV File Insight scans later, same result. MathType 6.9 claims compatibility with Windows 8.1, claims that multiple installation by one owner are permitted. What the heck? I've looked for other reports of the same problem all over the internet, can't find any. Anyone have a clue what is going on?