Here is some of the most pertinant info about the KLEZ, which I have copied and shortened from Trend Micro:
WORM_KLEZ
Details:
All KLEZ variants, except WORM_KLEZ.B, are mass-mailing worms. They mail themselves to specified addresses by sending SMTP commands to an SMTP server. The worm exploits a vulnerability that opens an executable attachment even in Microsoft Outlook's preview pane.
WORM_KLEZ.B enables a remote user access to its infected computer.
All KLEZ variants, except WORM_KLEZ.B, are multi-threaded worms, where each thread performs a predefined task such as network infection or emailing. WORM_KLEZ.B spawns multiple copies of itself in memory.
I. Propagation
Where it obtains target email addresses from:
KLEZ variants .A, .C, and .D obtain recipients from the entries in the default Windows Address Book (WAB). Variants .A, .E, .F, .G, .H, and .I also gather addresses from the following files in the infected computer: MP8, EXE, SCR, PIF, BAT, TXT, HTM, HTML, WAB, DOC, XLS, CPP, C, PAS, MPQ, MPEG, BAK, MP3.
The address used in the FROM field:
Variants A., .C, .D, .E, and .F take the address from a list that is stored in the worm body. The lists changes for each variant.
Variants .G, .H, and .I obtain email addresses to place in the FROM: field from the infected user's address book. This causes a non-infected user to appear as the person who has sent this worm's malicious email. It does this to hide the real sender of the infected email.
Mail Subject
Variants .A, .C, and .D compose the email subject line from a list in the worm's body. This list is the same for each of these three variants.
Variants .E and .F compose the email subject line from a list in the worm's body. This list is the same for variants .E and .F.
For variants .G, .H, and .I, the subject of the email is composed in a complex manner, but also taken from a list in the worm's body.
Mail Body
For variants .A, .C, and .D the message body is as follows:
I'm sorry to do so,but it's helpless to say sorry.
I want a good job,I must support my parents.
Now you have seen my technical capabilities.
How much my year-salary now? NO more than $5,500.
What do you think of this fact?
Don't call my names,I have no hostility.
Can you help me?
Variants .E, .F, .G, .H, and .I generate a random mail body
II. Payload
For variants .A, .C. and .D, on the 13th day of any odd month (January, March, May, July, September, November), the worm attempts to execute its destructive payload. For all fixed and remote drives, it overwrites all files with zeros. This worm routine has a bug in generating the drives, however, and therefore fails to perform the task. The size of the original file does not vary. For each drive the worm sleeps for 30 minutes.
For variants .E and .F, on the 6th day of any odd month, this worm searches the fixed and remote drives for files having the following extensions, and then attempts to overwrite these files with garbage code: TXT, HTM, HTML, WAB DOC, XLS, CPP, C PAS, MPEG, MPG, BAK, MP3, JPG.
Variants .B, .G, .H, and .I have no payload
III. Killing Antivirus Processes in Memory
Variants .A, .C, and .D kill running processes and occasionally delete the executable files of programs associated with some antivirus products. The list is the same for variants .A, .C, and D.
Variants .E, .F, .G, .H, and .I kill running processes and occasionally delete executable files of programs associated with some antivirus products. The list is the same for variants .E, .F and .H.
IV. Network Infection[/]b
The worm is capable of spreading via shared drives/folders with read/write access. ... For each entry, it copies itself to files with randomly generated filenames. Variants .A, .C, .E, .F, .G, .H, .I are capable of this. Variants .B and .D are not capable of network infection.
All I can say is Thank the good Lord that He gave me the brains to know not to use outlook for the last 10 years!! Even Netscape & Opera are immune from these particular viruses, btw. But you still need to scan for them and delete or fix the infected attachments. 