In many ways, the Internet resembles a fast-growing city that sprang up from a bucolic rural setting. In the span of a few short years, open fields have been transformed into a densely packed urban landscape peppered with all sorts of entertainment, resources, and opportunities. But there are also problems--like skyrocketing crime rates, shady neighborhoods, and street-savvy scam artists.
Firewalls can protect you from some, but not all, of these emerging urban Web threats. And in fact, the best defense against many of these threats is good judgment. If you see an e-mail offering an incredible deal or coming from someone you don't know, delete it. And never open attachments--even from trusted friends--unless you have a full understanding of the context. Many e-mail worms generate vaguely intriguing subject lines to entice users into launching malicious attachments, which are often disguised as digital photos or documents.
Here's an idea of what your PC faces every day on the Wild Wild Web.
Adware: Adware secretly tracks and gathers personal information--including sites you visit--and ships that data to a remote server for purposes of generating targeted advertisements. Many free, downloadable programs incorporate adware as a way to generate revenue.
Best defense: Anti-spyware software such as Spybot Search and Destroy or Lavasoft's Ad-Aware.
IP spoofing: Spoofing disguises packets so they appear to be coming from another source, typically a trusted host. Often used to gain unauthorized access to computers, IP spoofing can be defeated by a firewall that uses stateful packet inspection to peer into data packets to discern their true nature.
Best defense: A hardware firewall.
Phishing: A fast-growing form of online fraud, phishing describes sham e-mail broadcasts and Web sites that try to fool people into disclosing confidential data, such as passwords, credit card numbers, and social security numbers. A phishing e-mail may look like it's coming from a trusted vendor--say, your phone company--but in fact is from an unknown source.
Best defense: E-mail spam blocker such as IHateSpam or SpamKiller.
Port scanning: The digital equivalent of jiggling doorknobs, port scanning reveals open ports on Internet-connected PCs. Once an open port is found, a hacker can exploit the opening to try to break into the system or install malicious software.
Best defense: Hardware firewall.
Program exploits: This describes a wide variety of techniques designed to take advantage of a flaw or vulnerability in a piece of software, whether it is Windows XP, a Web browser, or an e-mail program. A popular exploit is buffer overflow, where a malicious application purposefully pours too much data into a buffer--a holding point for application data--in order to expose system resources to attack.
Best defense: Patching vulnerable software through services such as Windows Update.
Spyware: These applications secretly track system activity. Often bundled with legitimately useful software--such as the Kazaa Media Desktop client software--spyware can often transmit passwords or other confidential data to a remote computer.
Best defense: Anti-spyware software.
Trojan horse: This refers to a destructive program disguised to look like a useful application. For example, there has been a recent surge in Trojan horse applications posing as anti-spyware utilities. Users think they are downloading a useful utility, when in fact they are exposing their system to attack.
Best defense: Antivirus software such as Trend Micro's PC-cillin Internet Security 2004, anti-spyware software.
Virus: A virus is any malicious program or piece of code that replicates itself and attaches to a hard disk boot sector or partition, or to an application, document, macro, or other software medium. Viruses run the gamut from annoying applets that display innocuous messages to lethal attacks that delete hard disk contents and upload confidential information to remote servers.
Best defense: Antivirus software.
Worm: A worm is a type of virus that replicates itself but cannot attach itself to other programs. Worms may propagate by infecting a system and going through its e-mail contact list to broadcast e-mail with a worm-laden attachment to users on the list. Worms can also propagate by finding an open network port that allows entry to your system.
Best defense: Antivirus software, hardware firewall, e-mail spam blocker.
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