Malware and pirated ebooks

[MrSlow&Steady]

Originally Posted by Kindleing

Like a Zip file a rar file can contain multiple files. A poisoned rar file can contain a script which, when extracted, can infect a vulnerable computer. So someone thinks they are downloading an ebook but they are actually downloading malicious software. Many people aren't famiiar with rar files so it is easier to fool them.

Yeah I don't get why Rar files exist when Zip files already exist.

[ownedbycats]

RAR files have a few advantages. Higher compression (though 7z is better for this), being able to store NTFS filestreams, recovery records. I prefer them when making backups.

[Aleron Ives]

Zip is one of the oldest compression formats around, and newer compression formats and archivers are always being invented to try to save additional space or to add new features, such as LZMA (7-Zip, lzip) and zstd.

[theducks]

Originally Posted by MrSlow&Steady

I still don't get it.

RAR is a slightly more efficient compression for some types of files. There is also the need for NO compression on certain pieces so that the reading device knows what to do with the rest of the archive)

Think of all ARCHIVES as a Binding for the smaller pieces that make up the whole book. Pictures, chapters, display fonts (assumes device has the basic), Stylesheet, and the OPF to automatically direct the order chapters are displayed so you don't have to go to the index to click the next file (and like the CSS, it is a single place to set the orders)

Each archive file type has built in processing rules and limitations. Calibre only permits ONE of any file type to be stored in the Title folder (conflict management and other reasons), so it simply uses a different Archive type to package the book (very simplified explanation).

[arjaybe]

Originally Posted by MrSlow&Steady

Yeah I don't get why Rar files exist when Zip files already exist.

Do you get why Toyotas exist when Chevrolets already exist? Same thing.-)

[Quoth]

Or any other small car when a Yaris exists?

Or any small pickup when a Toyota pickup exists?

Why does the Musk Cybertruck exist?

[sgmoore]

Originally Posted by MrSlow&Steady

Yeah I don't get why Rar files exist when Zip files already exist.

That is like saying I don't get why Pepsi exists when Coke already exists or why Costa exists when Starbucks already exists.

<Old Man Mode>
Back in my day, before Windows existed, there were loads of competing compression programs and they all had advantages and disadvantages.

The zip format was invented by Phil Katz and his program was called pkzip and became popular because it was so much faster than other programs at that time. But one of the features that the original pkzip program was missing was the ability to handle zip files that were too big to fit on a floppy disk.

Arj and Rar files handled this better.

Also at the time of slow dialup modems and small hard disks, even a slight decrease in the size of file compressed file meant user saved money on their telephone bills and hosting servers also saved money. (As a comparison, my internet is over a hundred thousand times faster than my first dial-up modem).

But PK allowed anyone to write their own software to use his format for free which is why Microsoft added support for zip files in Windows without users needing to download additional software.

But many hosting sites still avoided zip files because the original program and Microsoft's implementation could not handle files over 4GB.

</Old Man Mode>

[haertig]

ZIP compresses individual files. These may then be bundled together into an archive, but they are still individually compressed files. You can pick and choose to extract only one file from a ZIP archive if you want.

RAR takes all the files it is given and compresses them into one blob. This enables it to find similarities that occur in different files and use that to achieve far better overall compression given files that contain similar stuff (human readable documents for example). This also means that you cannot extract a single file from a RAR archive. You have to extract them all, then ignore the ones you don't want. As a side effect, this might make RAR's better for spreading malware, since you can't pick and choose what specific contents you want to decompress. Certain utilities may make it appear that you can choose which files to decompress in RAR, but they're not really doing that under the hood. They're decompessing them all (as they have to with RAR) and then throwing out the files you don't want on your behalf.

[theducks]

Originally Posted by haertig

Certain utilities may make it appear that you can choose which files to decompress in RAR, but they're not really doing that under the hood. They're decompessing them all (as they have to with RAR) and then throwing out the files you don't want on your behalf.

I did not know WinRar was doing that. It just worked for what I wanted.

[Quoth]

Originally Posted by sgmoore

That is like saying I don't get why Pepsi exists when Coke already exists or why Costa exists when Starbucks already exists.

Yes, that's true and https://xkcd.com/927/

Originally Posted by sgmoore

As a comparison, my internet is over a hundred thousand times faster than my first dial-up modem).

1200 / 75 for Prestel like services in 1981-1982
300 only for real email, even in 1987 (via X25 PAD, a server and Bitnet)
I was on 8 Mbps down / 1 Mbps up (7.4 & 0.95 at peak time before fibre, 2005 to 2023).
Also errors meant dialup was slower. Even on 56K modem the line only did 19K (1998 to 2005, before that we had 128K ISDN for a few years).

So now 1.7 million times faster download and 170 thousand times faster upload than 1987.

[DNSB]

Originally Posted by MrSlow&Steady

I still don't get it.

Like using .zip, .7z, .tgz, etc., a .rar file can contain multiple files. Any of them can also contain malicious content. The use of .rar archives seems to be more popular in eastern Europe. They also seem to be popular with malware packagers likely since most malware checkers can check inside .zip files. When RAR archives were first implemented, there were quite a few features that were improvements on older archive formats. Most of those features are now common to modern archivers.

If you are interested, Wikipedia has a List of archive formats. I was surprised by how many of them I had used over the years going back to using CP/M.

[ownedbycats]

Originally Posted by haertig

RAR takes all the files it is given and compresses them into one blob. This enables it to find similarities that occur in different files and use that to achieve far better overall compression given files that contain similar stuff (human readable documents for example). This also means that you cannot extract a single file from a RAR archive. You have to extract them all, then ignore the ones you don't want.

Solid archive, 7z does it too, though I think the solid block option is halfway between completely solid and each file individually compressed. Higher compression, combined with the recovery record (7z doesn't have) and ability to store NTFS attributes, is why I prefer to use RAR for archiving/backup purposes.

Originally Posted by haertig

As a side effect, this might make RAR's better for spreading malware, since you can't pick and choose what specific contents you want to decompress.

Additionally: NTFS alternate data streams. You can use them to hide a file inside a different file. Usually they're discarded when a file moves between computers, but RAR can preserve them, which means that you can sneak malware in there. I think at least a few antiviruses make a point of checking them now.