Seeing File Types

If the lesson of the Trojan Horse has taught us anything, it's beware of Greeks bearing gifts. In today's world it applies to email attachments. One of the main problems with Windows is that by default, you do not know what is packaged in that email attachment. You have to turn this function on.

To do so (Windows 98), open "My Computer" and select View -> Folder Options -> View. Scroll down and uncheck the block that says, "Hide file extensions for known file types."

These "known" file types can contain viruses.

Files come in three types: "safe," "probably safe," and "you are asking for trouble." The following list is not all inclusive.

Safe Files

Among the safe files are text only files, graphic, video and sound files.

Text files that contain only text. They cannot harm you. If you open them, they will open in an application called notepad or maybe wordpad if they are big enough. Text only files have the following extensions: *.txt, *.log, *.ini. I don't know why the average person would want to mess with *.log or *.ini files, but looking at them won't do any harm.

Graphic files contain pictures. There are many formats, but the most common are *.jpg, *.gif, and *.bmp. One could put a virus in a graphic file, but you would have to change the file extension to execute it. Otherwise the application trying to open the picture will either just fail or give you a mungled picture.

Video files contain movies. Some of these formats are *.mpg, *.mov, *.avi and *.wmv.

Sound or audio files end in: *. aif, *.mid, *.mp3 and *.wav.

Probably Safe Files

These are files that contain macros. Mostly these are MS-Office files and the one most attacked is Word. Usually, viruses contained in these files are mostly nuisances. They usually stay within the application (that is, a Word virus won't affect an Excel file or other system files). If you are comfortable with the source of the file, it is probably safe to open it. These files end in *.doc, *.dot, *.xls, *.xlt, *.ppt. *.pot, and *.mdb. Zip files (*.zip) are safe to download and look at, but the contents are subject to the same caveats as any other file.

Beware of These Files

Any file that has an executable extension such as *.exe, *.scr, *.com, and even *.bat are most likely trouble. Unless you specifically requested these files from a reputable source, don't open them.

When in Doubt

If you feel like you need the file, download it to disk and run a virus scan on it. Do not launch it from your mail program.