hedwards: It's also the only reader that requires proper sandboxing. I rarely hear about exploits in other PDF readers. It's usually Acrobat because they decided that a display format needs to have scripts involved as well.
EDIT: Unless I'm missing something Foxit doesn't even have the capacity to execute scripts making sandboxing pointless.
Elenarie: As far as I know from what I've read online (I could be wrong), Foxit does support external scripting. Also, you have to consider the fact that Adobe's software is the most popular PDF reader / creator in the world, which results in it being targeted more (which in all honesty, I actually like, because security through obscurity is no security at all).
It's not security by obscurity, what I see on the Foxit website really shouldn't involve scripting. At least not in the reader version.
The reason why Adobe software is the most exploited software in the world, is because they coded it incompetently from the get go. MS Word suffers a similar problem where they decided that it would be really cool to integrate scripting into a document format. Doesn't work and it just leads to being exploited.
And don't get me started on Flash, granted Macromedia started that mess, but Adobe owns that one now.
This is a bit like saying, well, the fox has already eaten 5 of my chickens so we'd better let him continue guarding the hen house because he's probably full.