When you connect to the Internet, you have access to a vast network of resources and information. Unfortunately, you also expose yourself to security risks. These risks are (relatively) small if you access the Internet intermittently via dial-up. They increase if you are always connected to the Internet, as you may be via a DSL connection. There are Internet users -- generally known as "hackers" and "crackers" -- who may try to gain unauthorized access to your computer. Here are some of the more common methods they use:

• IP Spoofing
  Intruders look for the IP address of a trusted port, then modify the packet headers so they appear to originate from that port. (A packet is part of a message transmitted over a packet-switching network such as the Internet.)
  
  
• Port Surfing
  Basically, a port is a point of entry/exit on your computer. Hackers and crackers scan computers for open TCP/IP ports. They can use these open ports to connect to your system and gain access to your data. The more ports that are open on your computer, the greater the chance of intrusion.
  
  
• Viruses
  A virus is a piece of malicious code written by hackers and crackers to cause problems on a computer. They are often sent as email attachments such as executable programs, Word documents, and zip files. Viruses can also be hidden inside files or programs offered for download at Web pages. When the attachment or downloaded file is opened, the virus is activated. It then corrupts data on the infected computer and propagates itself. If you send an infected file to someone else, the virus may spread to that person's computer.
  
  
• Trojan Horse
  This type of destructive program is often sent as an email attachment, or masquerades as a harmless program. A Trojan horse sits on your computer and opens a portal. Intruders on the Internet scan for this portal, then use it to gain access to your system. NetBus and BackOrifice are two known Trojan horses.

Once hackers and crackers gain access to your computer, they can read information stored in your files, corrupt your data, or even crash your system.

Like any Internet connection (dial-up, ISDN, etc.), DSL is a means of transmission. It's the path intruders travel to reach your computer, much like the road burglars follow to reach your house. However, DSL carries a higher risk because of its constant "always on" connection. Also, the high speed of a DSL connection lets intruders download large files from your computer more easily than they could over a slower dial-up connection. And if you have a static IP address, intruders can more easily reconnect to your system.

Just as a homeowner is responsible for locking his doors and securing his house, you must secure your computer against intrusion. The most basic protection is to turn your modem off when not in use. Because hackers and crackers cannot reach your computer without a connection, your computer is safest when it--and its modem--is off.

There are several other ways you can minimize any risk:

• File and Print Sharing
• System Patches
• Server Use
• Virus Awareness
• Firewalls

File and Print Sharing
The Microsoft Windows operating system lets you share files and printing resources with other people, particularly on a Local Area Network (LAN). When you're online, your sharing network is extended to all Internet users--including hackers.

If you're running a single PC instead of a network of computers, you don't need file and print sharing. Here's how to disable it:

1. Right-click the Network Neighborhood icon on your desktop and choose Properties, or open your Start menu and choose Settings => Control Panel => Network.
2. Click the button labeled File and Print Sharing.
3. You'll see a dialog box that lists two sharing options; make sure both options are unchecked.
4. Click OK.

If you're running a network of computers or you need file and print sharing enabled to access certain resources, make sure they are protected by cryptic, hard to guess passwords. LAN users who must share files should bind NetBEUI to file and print sharing instead of TCP/IP.

For help on setting up a secure LAN, visit these sites:
xDSL Technology
Securing Your LAN

System Patches
Be sure to keep your operating system up to date with the latest security patches. You can visit the Microsoft Web site to download Windows 98 or Windows 95 patches. For Macintosh OS updates, visit the Apple Software Library.

Server Use
A server is a computer or program that manages network resources. A Web server pushes data to--and receives data from--the Internet on a 24-hour basis. Because Web servers open and listen for connections on many well-known port numbers, it's easy for hackers and crackers to scan across all potential ports.

Software such as Microsoft FrontPage lets you set up a Web server program on your computer. If you run a server program, your computer will look and act like a Web server to anyone on the Internet--and likely attract intrusion.

If you don't plan to use your computer as a Web server, you shouldn't run any server programs. If your computer will be used as a server, invest in anti-hacking software or a firewall to help keep your system safe.

Virus Awareness
Never download files or programs from sources you don't trust, or open email attachments sent from strangers.

For more protection, you should have an anti-virus program: software that seeks and removes harmful viruses and Trojan horses from your computer. McAfee VirusScan and Norton AntiVirus 2000 are two popular anti-virus programs.

Be sure to keep your anti-virus software up to date, and stay informed of the latest virus alerts and hoaxes.

Firewalls
To block intruders, install firewall software on your computer. A firewall intercepts and scans all traffic between the Internet and your computer. Any incoming traffic that doesn't meet specified security rules is denied and blocked, and the intruder's IP address is logged. You can trace the IP address at SamSpade.org:

1. In the first form field, enter the IP address.
2. Make sure the "Whois" box is checked.
3. Click "Do Stuff" to generate a Whois report.

The Whois report shows the domain name associated with the IP address. This will usually be the intruder's ISP. The report also provides administrative contact information, but you should visit the ISP's Web site (the domain name shown in the report) to learn how to report service abuse. Provide the intruder's ISP with the information in your firewall logs.

Personal firewalls such as Sybergen Secure Desktop™, BlackICE Defender, and Norton Internet Security 2000 offer good protection against hackers and crackers.

These security measures will help keep your computer system safe from intrusion. For more information--including an online security test--visit the Shields UP! Web site.