Some computers central to the operation of the Internet were subjected to "denial of service" attack on Monday.

Such an attack is effective against even well-protected computers, as it consists basically of other attacking computers connecting to it in huge numbers, sufficient to prevent the legitimate traffic from going through. Think of a hundred people all calling your home phone number at the same time. Try to get a call from someone you really want to hear from under those conditions.

This attack is often set up by infecting unprotected computers with stealth programs which, at a prearranged signal, begin bombarding the target address with requests for information. The owner of the computer, unless he is quite sophisticated, may never know that his machine has been "recruited" as a helpless digital weapon--a "zombie."

There isn't much we can do on our end to protect the big servers from attacks. We have to hope the operators are on the ball. However, to prevent your own machine from being used as a "zombie" to attack others, there are a couple of things you can do. A good anti-virus program and an effective firewall are musts, particularly for anyone who, like myself, is permanently hooked to the net. Norton has worked very well for me in the anti-virus and anti-Trojan area, and Zonealarm is an excellent firewall. The low-end version can be downloaded for free here. Some of Norton's packaged bundles also include a firewall program.

This is pretty much the extent of my not-too-extensive expertise. More info can be found here. Computer sorcerers like Steve Gibson and others deal with this stuff on a level so far above my head that the fish around me have lights on their noses.

I don't yet know the source of the recent attack, but I would guess that computers overseas in places like China, where security software is rare (some people have said that almost every computer in China is infected with viruses), would be quite vulnerable to being recruited as zombies.