This biggest sponsor of adware in the world is Google Adsense banner ads... there is no avoiding it. Even on the most legitimate of websites if they are hosting ads of any kind that are served dynamically, they could potentially be an adware download.
Additionally, toolbars and widgets are all just absolutely terrible.. For instance where I work everyone downloads The Weather Channels "WeatherBug" - WeatherBug for sure.. the biggest pile of crap adware, yet everyone is like.. It can't be bad it's from The Weather Channel. Well screw you WeatherChannel you adware sons of bitches... (*rant complete*)
Anyway, to get back on topic.. HTS is for the most part safe, and.. as a community website, it sometimes can not manage to moderate or be responsible for all the contest that could possible be posted or found in various areas... I'm sure that's in the disclaimer somewhere..