Error 42110 and Error 42120 and a Malware/Virus/Trojan Question

Full Scan was completed on my Mac with OS X Lion 10.7.5 + Avast!7.0 (39134) - scan report contains Warnings such as:
Error 42110 The file is a decompression bomb.
Error 42120 ARJ archive is corrupted.

Good Mac-Forum Experts,

Am regretful that I am so ignorant, but therefore, I need to ask you - -

  1. What is “a decompression bomb?” I mean, what are the issues, and what criteria would produce this classification on a file listed in OSX Lion’s Get Info panel as, Size: 131,722 bytes (4 KB on disk)? This file bootroot.loader, is found in the path,
    /System/Library/PrivateFrameworks/MediaKit.framework/Versions/A/Loaders/MKDrivers.bundle/Contents/Resources.
    and, does anybody know that this is a legitimate file, to find in that path in OS X v10.7.5?

  2. First, what is an ARJ archive? Does OS X Lion natively include any ARJ archives?

  3. One zip file was flagged with HTML:Bayfraud-AB [Trj]. Does Avast provide a KB or site that explains what its malware ID s (names like this one) are, in terms that enlighten us on the serious effects of the malwares? Is it possible that this is a Windows malware that does not harm our Macs? I also have in this report, something ID’d as W32:Gen or something like that, probably it is a Windows-targeted item, but can it hurt my Mac?

How is one to know which are Windows-only and harmless to Macs?

If these are too many questions for one posted query (although, not unrelated to each other), please illuminate my ignorance on any one of them…

TNX -
Falling Rock

Google is your friend.

http://forum.avast.com/index.php?topic=99361.0

http://www.surfing-safe.com/virus/avastproblem.php
"The errors below are about packed files, most of these errors are caused by a damaged archive, locked archive or unknown archive type. The best solution is to redownload the selected file "
2120 AVAST_PACK_ARJ_CORRUPTED ARJ is corrupted