Most probably you have been infected with the Trojan.IrcBounce. This trojan includes a copy of mIRC that hides as Taskmngr.exe (not to be confused with TASKMNG.EXE or TASKMAN.EXE) actually being mIRC32.exe version 5.7. The Trojan uses this file to run all of its mIRC scripts, including Dll32.hlp, Dll32NT.hlp, Xvpll.hlp, Httpsearch.ini, and NT32.ini. Read more, and detailed removal instructions at
http://securityresponse.symantec.com/avcenter/venc/data/trojan.ircbounce.html.
Note how this page tells you how the Norton virus scanner will remove the infection itself, but NOT the files in its payload. It will not remove mIRC or the registry setting starting mIRC! You'll have to do this yourself, by hand. The symantec info page provides all info you need to do that.Carefully read the section "
To delete from the registry the value that refers to Taskmngr.exe".
1. In windows, click the Start button, and click Run. The Run dialog box appears.
2. Type regedit and then click OK. The Registry Editor opens.
3. Navigate to the key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run
4. In the right pane, look for a value or value data that refers to Taskmngr.exe
5. Delete the reference if you find it.
6. Exit the Registry Editor.
Succes!