I used to be a big proponent of turning off the broadcasting of your WAP's SSID in order to hide it from would be hackers. The theory was turning off SSID broadcast makes it harder for outsiders to use your network since they would first have to guess your SSID. Since then, it was demonstrated to me just how simple and effective it is to use a wireless hacking program that can sniff out the SSID of a WLAN even if it is not being broadcast in the usual fashion. The program isn't particularly hard to find, so I've changed my viewpoint to hide it if you want to, but don't expect that will do much. I've also had trouble with some wireless Ethernet adapters (in laptops) reconnecting to the WLAN if the SSID broadcast is off.
In order to turn off the SSID broadcast, you'll need to find that setting in your router's configuration. For the WRT624, that setting is on the Advanced Wireless Settings page. Click on the Wireless Settings menu entry under the Advanced heading.
On the Advanced Wireless Settings screen, click on the Enable SSID Broadcast checkbox to clear it (so there is no "check" in the box) and hit the Apply button. If you go to the Networks tab of the WG511T wireless Ethernet adapter's configuration utility (as you did in the section Set the Wireless Ethernet Adapter's Channel and SSID to the WAP's New Settings), you will still see the Network name if you scan for networks. This is because that adapter already knew the name.
However, any adapter that did not already know the SSID of your network will see the following if they do a scan. The wireless adapter can see that there is a wireless network operating at the "G" speed on channel 6, but it can't determine the Network Name. Thus it is blank.
Not all hackers just want to use your wireless LAN; some want to monitor it to learn personal information, passwords, and credit card numbers. If your WLAN is operating in a small office, a hacker may be interested in learning your trade secrets, active court cases, or delivery schedule. Tools exist for hackers to capture and analyze your wireless network traffic without appearing to be connected to your WLAN. For these reasons, encrypting the traffic on your wireless LAN is almost essential. It also just happens to keep freeloading neighbors off your WLAN, too.
Initially, there was no encryption available on 802.11 networks as security was an optional part of the standard. Later, Wired Equivalent Privacy (WEP) encryption became available. However, WEP has some well-documented weaknesses that were found soon after its introduction. (Still, WEP is better than no encryption, and 128-bit WEP is better than 64/40-bit WEP.) Any hacker with enough time within range of your wireless network can capture enough wireless traffic to break WEP's encryption. WEP may keep the 10 year old next door off your WLAN, but nowadays, it won't even slow down anyone that is determined to compromise your wireless network. A decent WEP cracking program on a modest laptop can generally crack a WEP password in under 10 minutes.
Later versions of the 802.11 specification promoted Wi-Fi Protected Access (WPA) Pre-Shared Key (WPA-PSK) as the encryption protocol. WPA-PSK is much stronger than WEP while still based upon it, which let existing routers take advantage of it with only firmware upgrades. The next picture shows setting the WPA-PSK with the Netgear WRT624 using the Basic Wireless Settings page. (Remember to first set the wireless settings on the WAP and then go back and set the wireless Ethernet adapter to match.) Click on the radio button next to "WPA-PSK" and then enter a passphrase.
Unfortunately, WPA-PSK can also be compromised. A passphrase of 21 characters or more makes it significantly more difficult so long as a strong password (i.e., void of common dictionary words) is used. This is because WPA-PSK is particularly susceptible to dictionary attacks against passphrases. The passphrase can be to 63 characters in length. Making the phrase longer and more complex - using a mix letters (upper and lower case), numbers and special characters - makes the password significantly more difficult to crack. Another good practice is to substitute numbers for certain letters (that have the effect of spelling those letters backward). For example, use "3" instead of "E" or "e" and "1" instead of "I." Also, using special characters is very good. The passphrase "Th1s1s!MyP@55p4r@53UF00l" is a much stronger than "thisisnotmypassphraseyoufool" will ever be. Just be sure to remember what your scheme is. A newer WPA2 encryption protocol has since been added. It, too, can be compromised, but has technologies in it to make it much more difficult. If your wireless equipment supports WPA2 using that is more secure than WPA. WPA2 also comes in a couple of flavors: TKIP and AES. Both are good, but AES is better. AES requires reasonably up-to-date equipment, however.
Once the WAP has been set and the Apply button pressed, you will loose connectivity with your wireless LAN until the wireless Ethernet adapter has been changed to match the WAP's new settings. With the Netgear WG511T, this is done using the Settings tab in the Smart Configuration utility. Click on the Advanced radio button.
This will cause the Advanced Security dialog to appear. Enter the same passphrase you used for the WAP and press the OK button.