It was nice to know I wasn't the only one having problems installing Atlas April CTP due to cabinet file '_28942B4D9DE730210E7C27BD4FBAD377'...is corrupt.
I originally downloaded Atlas and did "Save As" (which is my habit, to install on multiple PCs). But as with quite a few others, it didn't work: "The cabinet file '_28942B4D9DE730210E7C27BD4FBAD377' required for this installation is corrupt and cannot be used. This could indicate a network error, an error reading from the CD-ROM, or a problem with this package."
I tried again, in both IE and FF, from my desktop and laptop (so four times) - clearing browser cache, etc (after the first time it broke, and I started googling for answers).
Then I noticed one of the comments on ASP.NET Atlas forum about the Publisher being 'Microsoft' versus 'Unknown', and it seemed like the versions I downloaded [Save As] and 'double-clicked' on were 'Unknown Publisher.
While not believing it would work , I tried again (with IE) BUT clicked [Run] instead... and the first dialog that appeared showed Publisher: Microsoft! The install worked fine from that point.
I don't know how/why the authenticode/whatever process would be different for a saved versus 'run straight away' install^, but after four failures across browsers/pcs and one success, I'd encourage others to at least give it a go -- click [Run] when you download!
^ actually, another post makes an interesting point about the effect of security/permissions in your IE 'downloads' folder versus your /My Documents/, /Desktop/ or wherever you might be placing the file when you [Save As]. I don't know enough about it to comment - but sounds feasible...?