istactivex.dll

hi have just scanned and located this trojan .is there gonna be any lasting efect or consequence of letting this on my system?

The file you mentioned seems to be part of a browser hijacker. I suggest you also run Ad-Aware, Spybot s&d and TheCleaner. It appears to me you also don’t use a firewall. www.zonelabs.com and www. kerio.com offer a free firewall. I suggest you install one of them. On this site (http://www.mvps.org/inetexplorer/info.htm) you can find more information. After downloading the progs I mentioned, update their databases 1st prior to run them. After running them, reboot and see if you still have a problem or not.

It appears to me you also don't use a firewall.
How can you tell that?