They're self installing malware droppers. They're Trojan horses. They display advertisements, change search results and open "back doors" to your system for other types of malware. They're also known as 28C6.TMP, B3B7.TMP, Alureon, TDSS and TDL. They originate from Portugal and Poland. Don't worry about it if your AV says they're cleared now though. Stuff like that just drops off the internet sometimes, you can't really help it.