Some thoughts on Computer Security

Information on the threats:

Spread of Windows-Based Trojan Horse Programs

In recent months, we have seen the spread of Windows-based Trojan horse programs. The most frequently reported incidents involving Windows-based Trojan horse programs involve the tools Back Orifice and NetBus.
We receive occasional reports of compromised machines that have one of these tools installed; however, the majority of reports involving these tools are from sites noticing intruders scanning their networks for the presence of these tools. We receive daily reports indicating that intruders are actively scanning networks to find running instances of these tools on already compromised machines.
Look for the following symptoms to detect those scans:
NetBus - connection request (SYN) packets to TCP port 12345
Back Orifice - UDP packets to port 31337
Keep in mind that these tools can be configured to listen on different ports. Because of this, we encourage you to investigate any unexplained network traffic.
Because these tools are Trojan horses, users must install them or be tricked into installing them. To impede the proliferation of this class of tools, we encourage system administrators to educate their users about safe computing practices (e.g., only install software from trusted sources, and use virus scanning software on any newly introduced software).
For more information about Back Orifice, we encourage you to review CERT Vulnerability Note VN-98.07, http://www.cert.org/vul_notes/VN-98.07.backorifice.html.

Widespread Scans

We continue to receive numerous daily reports of intruders using tools to scan networks for multiple vulnerabilities. On July 2, we published an incident note detailing this activity. This document is available at http://www.cert.org/incident_notes/IN-98.02.html
Since July 2 these tools have become a bit more sophisticated. Variants of the "mscan" tool now probe for the most recent vulnerabilities.Additionally, these tools incorporate the ability to identify a machine's architecture and operating system.

Scripted Tools

Very recently, we have received a few reports indicating that intruders are executing widespread attacks using scripted tools to control various information-gathering and exploitation tools. The combination of functionality used by the scripted tools enables intruders to automate the process of identifying and exploiting known vulnerabilities in specific host platforms. This information is available at http://www.cert.org/incident_notes/IN-98-06.html
 

Stealth Scanning Techniques

We have received a few reports indicating that intruders are using stealth scanning techniques. Stealth scanning is used by intruders to avoid detection. Details about stealth scanning techniques are available at http://www.cert.org/incident_notes/IN-98.04.html

Safe computing practices