The site itself is probably not installing anything to your site.  However, sites like that are itching for new advertisers all the time....the perfect opportunity for an "advertiser" to slip a malicious script into an ad.  Is the site at fault...kinda, because they're way too eager. 
What I recommend is not using those types of hosting methods to host your freebies.  There are still some very generous souls who will allow you to host your stuff.

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