In computing terminology, a ‘malicious code’ is a term used for computer viruses and programs designed to cause damage to computers. Other types of destructive PC worms are known as Internet virus including the examples like Worms and Trojans.
Outlined below is the description of different kinds of computer viruses:
Program/File Infector
Falling under the category of parasitic viruses, a program or file infector attempts to infect the files with extension code like .exe, .com, .drv, .dil, .bin, .ovl, and .sys. It gets activate along with the execution of executable file containing virus. The virus then loads itself into memory and replicates itself to other executable files when these files are opened or run.
The File Infector virus can destroy the content contained in files and cause irreversible damage to them. Some file viruses have also operated as email worm and Trojan horse.
The best way to disinfect files infected by the file virus is to delete them and restore from back up.
Macro Computer Virus
A macro computer virus is a virus written in a language built into a software application such as a word processor. For example: Microsoft Office has the macro language built into its application. This is why most of its application programs are affected by macro computer virus.
Macro viruses are generally created using the macro recorder or Visual Basic for Applications. The applications that are the most prone to this antivirus are Word Documents, Excel Spreadsheets, Power Point Presentation, and Access Database. The virus infects templates of these documents and therefore every file that the user opens gets affected. Some common macro computer viruses are Auto Exec, Auto New, Auto Open, Auto Close, and Auto Exit.
The auto macros can be disabled by using the command ‘DisableAutoMacros’ in any macro that is written. Another way to remove it is by holding down the shift key while opening a document.
Multi-Partite Virus
It behaves in the same way as other computer viruses do. As the name signifies, they are sometimes more than one type. These are hybrids and are known as multi-partite virus.
Polymorphic Viruses
It is a kind of virus which produces different but operational copies for itself. Its attack is considered to be extremely dangerous as virus detectors will not be able to detect all instances of virus attacks simultaneously. And this is one of the reasons why it is known to be strategically designed.
Stealth Viruses
A stealth virus uses different mechanisms to prevent recognition by antivirus software. It tries to escape detection either by redirecting the disk head to head to read another sector or modifying the file size shown in the Directory listing.
Classification of some viruses is not possible as they are the file type viruses which start behaving as computer worms with an activation code.
It's pretty clear that PDF files are the new "must use" when it comes to document handling. Who doesn't use a PDF nowadays? They are smaller than other similar files, can be viewed on Windows, Linux and MAC, and anyone can protect their PDF files with encryption and password. Because of the wide variety of free conversion tools available today, everybody can convert whatever files they want to PDF.
Students use a large variety of operating systems on their computers. Teachers can make sure that their courses will be viewed properly by converting them to PDF files. Universal deployment is maybe the most important asset of PDF format.
Companies and business users can keep their internal documents as PDF files, benefiting from their smaller size and making sure those files are read only by employees who know the password. PDF security is another important feature that made the PDF format so popular.
Finally, home users are using PDF files because Adobe did a very smart thing: Adobe Acrobat Reader is used only for viewing PDF files and is free. This way they made sure PDF format is available for everybody.
After PDF files became widely used, some new needs appeared. Users wanted to extract only a couple of pages from a PDF files. This could be done only by using dedicated software: a PDF splitter tool. Also, somebody at one point wanted to combine two or more PDF documents into a single file. They needed a PDF merger tool. Adobe made those tools, but they were not free. And because of their branding and marketing costs, those tools were pretty expensive.
Luckily, free tools emerged during time, but they were not developed by Adobe. Third party publishers made them available to public use, trying to gain a market share.
PDF Sam is the most popular tool that can be used to merge and combine PDF files. Originally started on the Source Forge platform, it is developed in Java and comes in two editions: a free one, and for those who donate any amount, an enhanced edition. It offers the basic PDF split and PDF merge operation, and in the enhanced version, file encryption.
Adolix Split and Merge PDF is quite a young entry in this market. Adolix developed this tool in Visual Basic, and focused on the graphical user interface. Their aim was to make it as user-friendly as posible. Following PDF Sam steps, Adolix's tool was first available as a free edition. Users could split and merge PDF files with just a few mouse clicks. At some point they also offered a Professional edition. Users could merge more than 5 files at once and split large documents into PDF files with the PRO version.
Other vendors also released tools to handle the split and merge PDF process. Adult PDF, Very PDF, AcroPDF and NitroPDF are only a few of the companies that entered the market with free or paid versions of those type of tools.