It took me a while to get my first virus but as some of you already know, it
happened not long ago
Well, it happened again, but things were a little bit worse this time.

A few days ago, my home network started acting up, mysteriously crawling to a
halt to the point where 90% of my packets couldn’t even reach my gateway. 
I soon identified the faulty machine and I disabled the network interface until
I had time to deal with the problem, because solving it would probably require
me to resort to a packet sniffer.  I finally found some time to investigate
the issue.

My first quick attempt was to selectively kill tasks and see if the network
comes back to normal, but this method didn’t produce any results.

The last time I used a packet sniffer was about fifteen years ago, on a Unix
machine.  If you’ve never used one, it’s quite enlightening, if not scary. 
Things have progressed quite a bit since that time but except for a fancy
graphic interface, the basic idea is the same:  your machine needs to be in
promiscuous mode (the default in Windows XP and 2000, which makes things easier
and is not a problem in a home network).  Of course, you need to be using a
hub ant not a switch, or you won’t be seeing all the packets broadcast through
your network.

A quick search revealed a host of packet sniffers on Windows and I settled on
AnalogX’s PacketMon.  It’s free, offers some basic filtering capabilities
and fits the bill for my simple problem.

I launched the program on another machine, re-enabled the network interface
on the patient and blam! the screen immediately starts scrolling at an alarming
rate.  The verdict was pretty clear:  my machine was sending a stream
of ICMP requests to IP addresses in decreasing order.  There is no better
way to spell "infected by a virus".

I downloaded an anti-virus, disabled the network interface and started the
long and painful scan.  In the meantime, I did some research on the Web and
based on the symptoms and the ports and packets used, my suspicion quickly
narrowed down on the

Welchia virus
, which the anti-virus quickly confirmed.

Fortunately, getting rid of it is straightforward and only requires a full
scan of your hard drive.  You can also download a separate

remover
which will accomplish the same job.

Interestingly, even after I removed the virus and confirmed with the packet
sniffer that everything was back to normal, my machine was still the target of a
lot of requests (both TMP and ICMP) from a wide variety of geographic locations. 
My firewall doesn’t have many ports open and since these requests were now
initiated from the outside, they were of no concern to me, but I ended up
wondering if these requests came from other randomly infected machines on the
Internet or if they were buddy machines that the virus had identified and
started exchanging information with.