Tojan horses

Trojan horses

A Trojan horse is a computer program which carries out malicious operations without the user's knowledge. The name "Trojan horse" comes from a legend told in the Iliad (by the writer Homer) about the siege of the city of Troy by the Greeks.

Legend has it that the Greeks, unable to penetrate the city's defences, got the idea to give up the siege and instead give the city a giant wooden horse as a gift offering.

The Trojans (the people of the city of Troy) accepted this seemingly harmless gift and brought it within the city walls. However, the horse was filled with soldiers, who came out at nightfall, while the town slept, to open the city gates so that the rest of the army could enter.

Thus, a Trojan horse (in the world of computing) is a hidden program which secretly runs commands, and usually opens up access to the computer running it by opening a backdoor. For this reason, it is sometimes called a Trojan by analogy to the citizens of Troy.

Like a virus, a Trojan horse is a piece of harmful code placed within a healthy program (like a false file-listing command, which destroys files instead of displaying the list).

A Trojan horse may, for example:

• steal passwords;
• copy sensitive date;
• carry out any other harmful operations;
• etc.

 

Worse, such a program can create an intentional security breach within your network, so as give outside users access to protected areas on the network.

The most common Trojan horses open machine ports, allowing their designer to gain entry to your computer over the network by opening a backdoor or backorifice.

A Trojan horse is not necessarily a virus, as its goal is not to reproduce itself to infect other machines. On the other hand, some viruses may also be Trojan horses; that is, they might spread like viruses and open ports on infected machines!

Detecting such a program is difficult because you must be able to determine whether an action is being carried out by the Trojan horse or by the user.

Symptoms of infection

 

Infection by a Trojan horse usually comes after opening a contaminated file containing the Trojan horse (see the article on protecting yourself from worms) and is indicated by the following symptoms:

• Abnormal activity by the modem, network adapter or hard drive: data is being loaded without any activity from the user;
• Strange reactions from the mouse;
• Programs opening unexpectedly;
• Repeated crashes.

Principle of a Trojan horse

 

As a Trojan horse is usually (and increasingly) intended to open a port on your machine so that a hacker can gain control of it (such as by stealing personal data stored on the hard drive), the hacker's goal is to first infect your machine by making you open an infected file containing the Trojan and then to access your machine through the opened port.

However, to be able to infiltrate your machine, the hacker normally has to know its IP address. So:

• Either you have a fixed IP address (as with businesses, or with individuals with a cable or similar connection, etc.) in which case your IP address can easily be discovered;
• or your IP address is dynamic (reassigned each time you connect), as with modem connections; in which case the hacker must scan IP addresses at random in order to detect those which correspond to infected machines.

Protect yourself from Trojans

 

Installing a firewall (a program which filters data entering and leaving your machine) is enough to protect you from this kind of intrusion. A firewall monitors both data leaving your machine (normally initiated by the programs you are using) and data entering it. However, the firewall may detect unknown outside connections even if a hacker is not specifically targeting you.. They may be tests carried out by your Internet service provider, or a hacker randomly scanning a range of IP addresses.

For Windows systems, there are two free high-performance firewalls:

• ZoneAlarm
• Tiny Personal Firewall

In case of infection

 

If a program whose origins you are unsure of attempts to open a connection, the firewall will ask you to confirm it before initiating the connection. It is important to not authorise connections for a program you don't recognise, because it might very well be a Trojan horse.

If this reoccurs, it may be helpful to check that your computer isn't affected by a Trojan, by using a program that detects and deletes them (called an anti-Trojan).
One example is The Cleaner, which can be downloaded from http://www.moosoft.com/.

List of ports commonly used by Trojans

 

Trojan horses commonly open a port on the infected machine and wait for a connection to open on that port, so that hackers will be able to gain total control over the computer. Here is a (non exhaustive) list of the most common ports used by Trojan horses (source: Site de Rico):

port	Trojan
21	Back construction, Blade runner, Doly, Fore, FTP trojan, Invisible FTP, Larva, WebEx, WinCrash
23	TTS (Tiny Telnet Server)
25	Ajan, Antigen, Email Password Sender, Happy99, Kuang 2, ProMail trojan, Shtrilitz, Stealth, Tapiras, Terminator, WinPC, WinSpy
31	Agent 31, Hackers Paradise, Masters Paradise
41	Deep Throat
59	DMSetup
79	FireHotcker
80	Executor, RingZero
99	Hidden port
110	ProMail trojan
113	Kazimas
119	Happy 99
121	JammerKillah
421	TCP Wrappers
456	Hackers Paradise
531	Rasmin
555	Ini-Killer, NetAdmin, Phase Zero, Stealth Spy
666	Attack FTP, Back Construction, Cain & Abel, Satanz Backdoor, ServeU, Shadow Phyre
911	Dark Shadow
999	Deep Throat, WinSatan
1002	Silencer, WebEx
1010 to 1015	Doly trojan
1024	NetSpy
1042	Bla
1045	Rasmin
1090	Xtreme
1170	Psyber Stream Server, Streaming Audio Trojan, voice
1234	Ultor trojan
port 1234	Ultors Trojan
port 1243	BackDoor-G, SubSeven, SubSeven Apocalypse
port 1245	VooDoo Doll
port 1269	Mavericks Matrix
port 1349 (UDP)	BO DLL
port 1492	FTP99CMP
port 1509	Psyber Streaming Server
port 1600	Shivka-Burka
port 1807	SpySender
port 1981	Shockrave
port 1999	BackDoor
port 1999	TransScout
port 2000	TransScout
port 2001	TransScout
port 2001	Trojan Cow
port 2002	TransScout
port 2003	TransScout
port 2004	TransScout
port 2005	TransScout
port 2023	Ripper
port 2115	Bugs
port 2140	Deep Throat, The Invasor
port 2155	Illusion Mailer
port 2283	HVL Rat5
port 2565	Striker
port 2583	WinCrash
port 2600	Digital RootBeer
port 2801	Phineas Phucker
port 2989 (UDP)	RAT
port 3024	WinCrash
port 3128	RingZero
port 3129	Masters Paradise
port 3150	Deep Throat, The Invasor
port 3459	Eclipse 2000
port 3700	portal of Doom
port 3791	Eclypse
port 3801 (UDP)	Eclypse
port 4092	WinCrash
port 4321	BoBo
port 4567	File Nail
port 4590	ICQTrojan
port 5000	Bubbel, Back Door Setup, Sockets de Troie
port 5001	Back Door Setup, Sockets de Troie
port 5011	One of the Last Trojans (OOTLT)
port 5031	NetMetro
port 5321	FireHotcker
port 5400	Blade Runner, Back Construction
port 5401	Blade Runner, Back Construction
port 5402	Blade Runner, Back Construction
port 5550	Xtcp
port 5512	Illusion Mailer
port 5555	ServeMe
port 5556	BO Facil
port 5557	BO Facil
port 5569	Robo-Hack
port 5742	WinCrash
port 6400	The Thing
port 6669	Vampyre
port 6670	Deep Throat
port 6771	Deep Throat
port 6776	BackDoor-G, SubSeven
port 6912	Shit Heep (not port 69123!)
port 6939	Indoctrination
port 6969	GateCrasher, Priority, IRC 3
port 6970	GateCrasher
port 7000	Remote Grab, Kazimas
port 7300	NetMonitor
port 7301	NetMonitor
port 7306	NetMonitor
port 7307	NetMonitor
port 7308	NetMonitor
port 7789	Back Door Setup, ICKiller
port 8080	RingZero
port 9400	InCommand
port 9872	portal of Doom
port 9873	portal of Doom
port 9874	portal of Doom
port 9875	portal of Doom
port 9876	Cyber Attacker
port 9878	TransScout
port 9989	iNi-Killer
port 10067 (UDP)	portal of Doom
port 10101	BrainSpy
port 10167 (UDP)	portal of Doom
port 10520	Acid Shivers
port 10607	Coma
port 11000	Senna Spy
port 11223	Progenic trojan
port 12076	Gjamer
port 12223	Hack�99 KeyLogger
port 12345	GabanBus, NetBus, Pie Bill Gates, X-bill
port 12346	GabanBus, NetBus, X-bill
port 12361	Whack-a-mole
port 12362	Whack-a-mole
port 12631	WhackJob
port 13000	Senna Spy
port 16969	Priority
port 17300	Kuang2 The Virus
port 20000	Millennium
port 20001	Millennium
port 20034	NetBus 2 Pro
port 20203	Logged
port 21544	GirlFriend
port 22222	Prosiak
port 23456	Evil FTP, Ugly FTP, Whack Job
port 23476	Donald Dick
port 23477	Donald Dick
port 26274 (UDP)	Delta Source
port 27374	SubSeven 2.0
port 29891 (UDP)	The Unexplained
port 30029	AOL trojan
port 30100	NetSphere
port 30101	NetSphere
port 30102	NetSphere
port 30303	Sockets de Troie
port 30999	Kuang2
port 31336	Bo Whack
port 31337	Baron Night, BO client, BO2, Bo Facil
port 31337 (UDP)	BackFire, Back Orifice, DeepBO
port 31338	NetSpy DK
port 31338 (UDP)	Back Orifice, DeepBO
port 31339	NetSpy DK
port 31666	Bo Whack
port 31785	Hack�a�Tack
port 31787	Hack�a�Tack
port 31788	Hack�a�Tack
port 31789 (UDP)	Hack�a�Tack
port 31791 (UDP)	Hack�a�Tack
port 31792	Hack�a�Tack
port 33333	Prosiak
port 33911	Spirit 2001a
port 34324	BigGluck, TN
port 40412	The Spy
port 40421	Agent 40421, Masters Paradise
port 40422	Masters Paradise
port 40423	Masters Paradise
port 40426	Masters Paradise
port 47262 (UDP)	Delta Source
port 50505	Sockets de Troie
port 50766	Fore, Schwindler
port 53001	Remote Windows Shutdown
port 54320	Back Orifice 2000
port 54321	School Bus
port 54321 (UDP)	Back Orifice 2000
port 60000	Deep Throat
port 61466	Telecommando
port 65000	Devil