im speaking from experiance when i say trojan codes run right through avg,norton macafee and they will run backup files inside other directorys, you need to start in safe mode under administrator acc if there is one just safe mode nothting else then quiet simply run a search by searching in your pc for whatever the error box says and try not to click ok as there most times a trigger to reinstall untill its free again, try checking inside firewall allowed ports and so on for anything that isnt been added by yourself you can use microsoft security essentials then one part of the trojan is gone it will be visable to the system as broken linked installation program.
some really stupid ones are security.exe inside system32 but a trojan is real easy to remove just as long as you dont click error boxes when your pc starts up or trying to run a program.
hope thats helped you some m8 good luck