File downloads and types
There are a number of file types that are fairly harmless, because they cannot possibly carry any sort of malware. A malicious program would have to be in an executable file of some sort. Being aware of the dangerous file extensions will go a long way in protecting a system.
Malware requires some sort of executable code to run, and therefore infest a system. These come in a variety of disguises; some not as obvious as the others. Of course, the standard executable file extensions like .exe, .bat and .com are prime suspects. However there are others as well: .vbs, a Visual Basic Scripting file; .pif and .cmd, which can control DOS applications.
Even .doc, .ppt, .xls and .rtf files are dangerous. This may seem odd, until one remembers that all the Microsoft Office applications have the option of macros and embedded Visual Basic scripts. Those are types of code as well, and as a result, risky also. The rich text format or .rtf files are essentially Word documents with changed extensions so should be treated in much the same way.
When downloading any sort of file, it is best to avoid ones that require an application to open it. Text files or HTML files are safe ones to work with since they do not have any scripting or code that could potentially harm the system.