I. The Why
There is an average of 10-20 viruses released every day. Very few of these viruses actually make “Wild” stage. Viruses are designed to take advantage of security flaws in software or operating systems. These flaws can be as blatant as Microsoft Windows NetBIOS shares to exploits using buffer overflows. Buffer overflows happen when an attacker sends responses to a program longer then what is expected. If the victim software is not designed well, then the attacker can overwrite the memory allocated to the software and execute malicious code.
People make viruses for various reasons. These reasons range from political to financial to notoriety to hacking tools to plain malicious intent.
Political: Mydoom is a good example of a virus that was spread with a political agenda. The two targets of this virus were Microsoft and The SCO Group. The SCO Group claims that they own a large portion of the Linux source code threatened to sue everyone using Linux operating systems (with “stolen” programming source). The virus was very effective knocking down SCO’s website. However, Microsoft had enough time to prepare for the second attack and efficiently sidestepped disaster.
Financial: Some virus writers are hired by other parties to either leach financial data from a competitor or make the competitor look bad in the public eye. Industrial espionage is a high risk/high payout field that can land a person in prison for life.
Notoriety: There are some that write viruses for the sole purpose of getting their name out. This is great when the virus writers are script kiddies because this helps the authorities track them down. There are several famous viruses that have the author’s email in the source code or open script
Hacking Hackers sometimes write controlled viruses to assist in the access of a remote computer. They will add a payload to the virus such as a Trojan horse to allow easy access into the victims system.
Malious: These are the people that are the most dangerous. These are the blackhat hackers that code viruses for the sole intention of destroying networks and systems without prejudice. They get high on seeing the utter destruction of their creation, and are very rarely script kiddies.
Many of the viruses that are written and released are viruses altered by script kiddies. These viruses are known as generations of the original virus and are very rarely altered enough to be noticeable from the original. This stems back to the fact that script kiddies do not understand what the original code does and only alters what they recognize (file extension or victim’s website). This lack of knowledge makes script kiddies very dangerous.
II. The How
Malicious code has been plaguing computer systems since before computers became a common household appliance. Viruses and worms are examples of malicious code designed to spread and cause a system to perform a function that it was not originally designed to do.
Viruses are programs that need to be activated or run before they are dangerous or spread. The computer system only becomes infected once the program is run and the payload has bee deployed. This is why Hackers and Crackers try to crash or restart a computer system once they copy a virus onto it.
There are four primary ways worms and viruses spread:
1.) Email
2.) Network connectivity
3.) Downloading or installing software
4.) Inserting infected media
Spreading through Email
Many emails spread when a user receives an infected email. When the user opens this email or previews it, the virus is now active and starts to immediately spread.
Spreading through Network
Many viruses are network aware. This means that they look for unsecured systems on the network and copy themselves to that system. This behavior destroys network performance and causes viruses to spread across your system like wildfire. Hackers and Crackers also use Internet and network connections to infect systems. They not only scan for unprotected systems, but they also target systems that have known software vulnerabilities. This is why keeping systems up to date is so important.
Spreading through manual installation
Installing software from downloads or disks increase the risk of infection. Only install trusted and scanned software that is known to be safe. Stay away from freeware and shareware products. These programs are known to contain Spyware, Adware, and viruses. It is also good policy to deny all Internet software that attempts to install itself unless explicitly needed.
Spreading through boot sectors
Some viruses corrupt the boot sector of disks. This means that if another disks scans the infected disk, the infection spreads. Boot sector viruses are automatically run immediately after the disk is inserted or hard drive connected.
III. Minimizing the effect of viruses and worms
We have all heard stories about the virus that destroyed mission critical company data, which cost companies months to recover and thousands of dollars and man-hours restoring the information. In the end, there are still many hours, costs, and would be profits that remain unaccounted. Some companies never recover fully from a devastating attack. Taking simple precautions can save your business
Anti-virus Software
Another step is to run an antivirus program on the local computer. Many antivirus programs offer live update software and automatically download the newest virus definitions minutes after they are released (Very important that you verify these updates weekly if not daily). Be careful of which antivirus program you chose. Installing a PC antivirus on a network can be more destructive on performance than a virus at work. Norton makes an effective corporate edition specifically designed for Windows NT Server and network environments. When using antivirus software on a network, configure it to ignore network drives and partitions. Only scan the local system and turn off the auto protection feature. The auto-protect constantly scans your network traffic and causes detrimental network issues. Corporate editions usually have this disabled by default. PC editions do not.
Email Clients
Do not open emails from unknown sources. If you have a website for e-commerce transactions or to act as a virtual business card, make sure that the emails come up with a preset subject. If the emails are being sent through server side design instead of the users email client, specify whom it is coming from so you know what emails to trust. Use common sense when looking at your email. If you see a strange email with an attachment, do not open it until you verify whom it came from. This is how most MM worms spread.
Disable preview panes in email clients. Email clients such as Outlook and Outlook Express have a feature that will allow you to preview the message when the email is highlighted. This is a Major security flaw and will instantly unleash a virus if the email is infected.
It is also a good idea to turn off the feature that enables the client to view HTML formatted emails. Most of these viruses and worms pass by using the html function “” and run the attached file within the email header.
We will take a quick look at an email with the subject header of “You’re now infected” that will open a file called readme.exe.
Subject: You’re now infected
MIME-Version: 1.0
Content-Type: multipart/related;
type=”multipart/alternative”;
boundary=”====_ABC1234567890DEF_====”
X-Priority: 3
X-MSMail-Priority: Normal
X-Unsent: 1
To: undisclosed-recipients:;
–====_ABC1234567890DEF_====
Content-Type: multipart/alternative;
boundary=”====_ABC0987654321DEF_====” *** (This calls the iframe)
–====_ABC0987654321DEF_====
Content-Type: text/html;
charset=”iso-8859-1″
Content-Transfer-Encoding: quoted-printable
*** (This calls readme.exe)
–====_ABC0987654321DEF_====–
–====_ABC1234567890DEF_====
Content-Type: audio/x-wav;
name=”readme.exe” *** (This is the virus/worm)
Content-Transfer-Encoding: base64
Content-ID: *** (Notice the )
PCFET0NUWVBFIEhUTUwgUFVCTElDICItLy9XM0MvL0RURCBIVE1MIDQuMCBUcmFuc2l0aW9u
YWwvL0VOIj4NIDxodG1sPg08aGVhZD4NPHRpdGxlPldobydzIHRoZSBiZXN0LS0tLS0tPyAt
IHd3dy5lemJvYXJkLmNvbTwvdGl0bGU+DQ0NDTxzY3JpcHQgbGFuZ3VhZ2U9amF2YXNjcmlw
dCBzcmM9aHR0cDovL3d3dzEuZXpib2FyZC5jb20vc3BjaC5qcz9jdXN0b21lcmlkPTExNDc0
NTgwODI+PC9zY3JpcHQ+DTxzY3JpcHQgbGFuZ3VhZ2U9ImphdmFzY3JpcHQiPg08IS0tDWZ1
bmN0aW9uIE1NX29wZW5CcldpbmRvdyh0aGVVUkwsd2luTmFtZSxmZWF0dXJlcykgeyAvL3Yy
*** Broken to protect the innocent. (Worm is encoded in Base64)
aHJlZj1odHRwOi8vY2l0YWRlbDMuZXpib2FyZC5jb20vZmNhbGhpc3BvcnRzZnJtMT5Gb290
YmFsbDwvYT4NIA08Zm9udCBjb2xvcj0jRkYwMDAwPiAtIDwvZm9udD4NDTxicj48YnI+PGJy
Pjxicj5Qb3dlcmVkIEJ5IDxhIGhyZWY9aHR0cDovL3d3dy5lemJvYXJkLmNvbS8+ZXpib2Fy
ZK48L2E+IFZlci4gNi43LjE8YnI+Q29weXJpZ2h0IKkxOTk5LTIwMDEgZXpib2FyZCwgSW5j
Lg08L2NlbnRlcj4NPC9ib2R5Pg08L2h0bWw+DQ0NDQoNCj==
–====_ABC1234567890DEF_====–
Email Servers
The first step to minimizing the effect of viruses is to use an email server that filters incoming emails using antivirus software. If the server is kept up to date, it will catch the majority of Mass Mailer (MM) worms. Ask your Internet Service Provider (ISP) if they offer antivirus protection and spam filtering on their email servers. This service is invaluable and should always be included as the first line of defense.
Many companies house an internal email server that downloads all of the email from several external email accounts and then runs an internal malware/SPAM filter. Combining an internal email server with the ISP protection is a perfect for a company with an IT staff. This option adds an extra layer of control, but also adds more administration time.
Software Updates
Keep you software up to date. Some worms and viruses replicate through vulnerabilities in services and software on the target system. Code red is a classic example. In august 2001, the worm used a known buffer overflow vulnerability in Microsoft’s IIS 4.0 and 5.0 contained in the Idq.dll file. This would allow an attacker to run any program they wanted to on the affected system. Another famous worm called Slammer targeted Microsoft SQL Server 2000 and Microsoft Desktop Engine (MSDE) 2000.
When updating your software, make sure to disable features and services that are not needed. Some versions of Windows have a web server called IIS installed by default. If you do not need these services, make sure they are turned off (Code red is a perfect example). By only enabling services you need, you decrease the risk of attack.
Telecommunications Security
Install a firewall on the network. A firewall is a device or software that blocks unwanted traffic from going to or from the internal network. This gives you control of the traffic coming in and going out of your network. At minimum, block common ports 135,137,139,445. This stops most network aware malware from spreading from the Internet. However, it is good practice to block all traffic unless specifically needed.
Security Policies
Implementing security policies that cover items such as acceptable use, email retention, and remote access can go a long way to protecting your information infrastructure. With the addition of annual training, employees will be informed enough to help keep the data reliable instead of hinder it. Every individual that has access to your network or data needs to follow these rules. It only takes one incident to compromise the system. Only install proven and scanned software on the system. The most damaging viruses come from installing or even inserting a contaminated disk. Boot sector viruses can be some of the hardest malware to defeat. Simply inserting a floppy disk with a boot sector virus can immediately transfer the virus to the hard drive.
When surfing the Internet, do not download untrusted files. Many websites will install Spyware, Adware, Parasites, or Trojans in the name of “Marketing” on unsuspecting victims computers. Many prey on users that do not read popup windows or download freeware or shareware software. Some sites even use code to take advantage of vulnerability in Internet explorer to automatically download and run unauthorized software without giving you a choice.
Do not install or use P2P programs like Kazaa, Morpheus, or Limewire. These programs install server software on your system; essentially back dooring your system. There are also thousands of infected files floating on those networks that will activate when downloaded.
Backups & Disaster Recovery Planning
Keep daily backups offsite. These can be in the form of tape, CD-R, DVD-R, removable hard drives, or even secure file transfers. If data becomes damaged, you would be able to restore from the last known good backup. The most important step while following a backup procedure is to verify that the backup was a success. Too many people just assume that the backup is working only to find out that the drive or media was bad six
months earlier when they were infected by a virus or lost a hard drive. If the data that you are trying to archive is less then five gig, DVD-R drives are a great solution. Both the drives and disks have come down in price and are now a viable option. This is also one of the fastest backup methods to process and verify. For larger backups, tape drives and removable hard drives are the best option. If you choose this method, you will need to rotate the backup with five or seven different media (tapes, CD/DVD, removable drives) to get the most out of the process. It is also suggested to take a “master” backup out of the rotation on a scheduled basis and archive offsite in a fireproof safe. This protects the data from fire, flood, and theft.
In the Internet age, understanding that you have to maintain these processes will help you become successful when preventing damage and minimizes the time, costs, and liabilities involved during the disaster recovery phase if you are affected.
Jeremy Martin
Information Warfare Engineer