Periodically dropped packets to router?

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Hey guys, I've recently acquired a problem on my personal computer. I keep getting dropped packets to my router on a regular basis.

When it began: it began on a day AVG popped up telling me it had found trojan activity. First time I've ever had a resident protection program do anything. Okay, I cleaned it up, and scanned with various other programs afterwards. The next day, AVG had found ANOTHER problem, a worm. Okay, I cleaned that up, and scanned with more programs again and found nothing else. Ever since then however I've been getting as much as 6% packet loss to the router over hours of pinging it to test stability. My other computer here is having no problem yet.

So, one computer drops no packets at all, but it seems when the computer with problems is running the entire network is affected. I looked at the router and I see DoS attacks (Ascend Kill, RTS Scan). The Ascend Kill attacks are coming from my computer, and the RTS Scan attacks are coming from various IPs. There aren't a whole lot of these in the log at the moment, and I have stateful packet inspection on my router turned on.

Short of reinstalling my OS which I haven't had to do on this computer in close to 2 years, I'm out of ideas. I've tried a lot of stuff to fix the problem and have scanned with various programs and I'm at my wits end.

Anyone here have any ideas for me to look into? I hope so, and thanks for any suggestion!

#1, backup your stuff now.

Proceeding under the following assumption: You are using a Micro$oft Windows OS.

You seem savvy, grab Ethereal or Wireshark and examine the packets this system is sending out in realtime.

Also, many modern viruses will attack anti-virus programs first so AVG may be somewhat unreliable. If AVG is running and updated, you may want to update/reinstall your NIC driver and nose around in System and App logs to make sure nothing is amiss in there.

If this fails and you don't have a factory image, see if it will even let you do a System Restore or if the restore points are hosed. Roll it back as far as it will let you.

If there is still something wrong, run HJT (HijackThis) and check the logs for anomalous progs running in the background. But BE CAREFUL deleting anything unless you know what you're about.

REINSTALL ADVICE:
Worst case, a reinstall even from disk will take you maybe two hours and most of that is twiddling your thumbs waiting for files to copy. While your one system is formatting, copying, etc. use the other system to download the drivers to a USB drive (make SURE this is not infected) so you can just plug it in and install everything. Start with anything onboard (chipset, audio, maybe video) and then proceed to the other drivers. If you've got a Dell make sure to install "Notebook/Desktop System Software" before everything else. Also, you might as well take the time to update your BIOS. When you get it up and running, the first thing to do is install all current patches from Windows Update and then follow up with throwing on AVG again, updating it immediately before you go ANYWHERE online.

Make a list of all the most critical/safest applications you use in the add/remove programs list. Dont forget your virus scanner. You can even download service packs as an installer through firefox.

One the second machine download copies of these, as well as drivers as was said. Put them on an external hard drive with no operating system present.

Copy all your personal data onto the external hard drive with NO operating system present. You want to avoid any executable or installed files being transfered from your current windows install.

Follow this ladies instructions: http://www.youtube.com/watch?v=9h3q5ss40oY

But you want to scan the external instead of the windows partition in her instructions.

All done? Disconnect the external drive.

Disconnect your lan or router. That means no cable attached, or no power at least. No internet at all is what you are aiming for.

Now reinstall windows from scratch. Once that is done, install services packs and then install your list of critical applications from the external drive. Still no internet.

You'll need to register your activation key usage, so plug in the internet briefly and do this. The alternative is to get on the phone with customer service... nah! Unplug the external for this step. Is there a no write switch on external drives?

Now back to the linux liveCD. Use this to copy your whole new install onto the external drive. It will take a while..

And when you are done you will have a fresh fully outfitted install. It should be virus free, and you will have an back up copy that is identical and already registered. If your working copy gets corrupted or infected, just copy from the external.

Now.. assuming that you are finding new things to install, you want to add them in to your archive safely. The best thing to do is keep a new list and next time you copy from the archive, immediately install that application and copy it back to the archive.

I'd pay for a decent AV like Avira. I guess you're not using a full version of AVG. If you use a free AV, only Avast had a full free version last time I checked.

If you haven't nuked and paved yet, restart in Safe Mode (NOT Safe Mode with Networking) and run a scan. First, though, find and download WINSOCK repair program. I'm quite certain this virus has attached itself as a filter in your TCP/IP stack, and removing it will break networking entirely.