You got a Trojan.Downloader
However, it's not very easy to know which, or where to look when you don't know when it happened.
Have you tried: msconfig > startup > look for files which are suspicious (it's relatively easy to find if you've had viruses before).
You could then google the file names (eg. ultrahax.exe) you find suspicious, your results should be several websites which declares if it's a virus or not.
About the Trojan.Downloader: it's a really tiny file that could either come from a website (unnoticed download by being compressed inside an image or .ico file), or an installation of an application.
It puts itself on the startup list, and downloads updated malware.
There are two reasons to why they keep appearing, one is the above.
Second, it's still on startup, but it's a process, which constantly checks if their files (viruses etc..) exists.
If it doesn't, he goes "let's re-extract them from myself, wohoo!".
Safe Mode + Full admin-right scan with Avira Antivir, Malwarebytes Anti Malware, NOD32, AVG should be able to fix it.
If it doesn't, try the msconfig I tipped you about.
As for everyone else screaming "boot scan!"...
No, this isn't an error in the boot section, as his operating system loads, OH WELL.
