Virus Problem In Windows 7????Low Internet Speed???????

I have windows 7 build 7600 installed. I also have an unlimited internet connection with a maximum speed of 256 kbps(which I rarely gets). Two-Three weeks ago I tried to download a file via torrent and suddenly its speed decreased. And when I checked after sometimes I also found that my entire Internet speed had... show more I have windows 7 build 7600 installed.
I also have an unlimited internet connection with a maximum speed of 256 kbps(which I rarely gets).
Two-Three weeks ago I tried to download a file via torrent and suddenly its speed decreased.
And when I checked after sometimes I also found that my entire Internet speed had reduced to half(almost 30-35 kbps). I often get 60-70 kbps always although I have a max. speed of more than that.
I suspect a virus Might Have done it...Two months back when I try to download the same file(OSCAR Award Function) I got this exact same problem... Now only I understand that it is because of this file.. But it was solved then when some anti-spyware/malware/adware software detected a backdoor.trojan and I removed it.
Now I cannot detect it...
I used the following antivirus turn by turn.
Avast Internet Security 5.
Bitdefender Total Security 2010.
Kaspersky Internet Security 2010.
And Also The Following anti-spyware/malware/adware softwares.
Malwarebytes' Anti-Malware.
Free Spyware Adware Scanner Remover
Spybot - Search & Destroy
And some other softwares too.


PS.Yesterday when I was running too many programmes including a download manager(Internet Download Manager/IDM) all the programmes became unresponsive except IDM(Maybe because it consumes less memory). Every programme including explorer.exe restarted.On my screen was IDM at that time and when I saw its speed I was really shocked It was upto 140 kbps...


PLEASE HELP ME IF YOU CAN...........................
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