A good rule of thumb is to always be suspicious of unknown software you receive as an e-mail attachment, find on untrustworthy Web or FTP sites, or receive as a Java applet or ActiveX item embedded in an unfamiliar Web page. A computer is also at some risk from attacks by Internet hackers who use probing software to locate vulnerable systems. A full-time connection and a static IP address can heighten your vulnerability to these hackers by making your computer available to them 24 hours a day. However, Macs running OS 9 or earlier with default settings aren't nearly as vulnerable to these attacks as Unix workstations. It's a different story if your Macintosh provides services over the Internet.
Firewall software offers additional protection against hackers.
For those who share an Internet connection on a local network, most software packages include a firewall that blocks unsolicited access to computers on local networks. The Extensions Manager control panel in Mac OS 7.6 and later can list and sort items by package, but items may end up in the wrong package or no package at all. For instance, I created my own Printers package. To change an extension's package, make a copy of the extension and then use ResEdit to open the original version from your Extensions folder. Double-click the vers icon, and open the resource with ID 2.