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Common sense and a basic knowledge of a few DOS commands are the best weapons against computer viruses. Tips and procedures to help prevent, detect or eliminate viruses include: understanding the meaning and operation of viruses and Trojan horse programs, using software from reliable sources, always downloading data from another computer to a floppy disk instead of a hard disk, checking the DOS directory periodically using the CHKDSK command, maintaining up-to-date hard copy of directories and their contents, sorting subdirectories by date, time, file size, file name and file extension; always using DOS FORMAT command to recycle a floppy disk, preparing a clean boot disk, preparing a clean disk contain at least the DOS files, and removing suspicious files with a suggested utility.

In most cases, your best weapons against computer viruses are common sense and a basic knowledge of a few DOS commands. If you're unfamiliar with DOS commands, see the "Journey Through DOS" series that appeared in the October, November, and December issues of LOTUS. The following tips and procedures should help you prevent viruses or, failing that, detect and eliminate them.

* Understand the meaning and operation of virus and Trojan horse programs. The seeding of a virus from one system to another is a separate event from the operation of any destructive code the virus may implant. For example, Trojan horse programs execute with the first access; viruses wait for a signal to execute: a specific date or the nth access of a target file.

* Use software from reliable sources. If you use public domain, shareware, or freeware programs, contact the writer or distributor and compare the file date and file size before using. If the software does not include a contact address or phone number, DO NOT use it.

* When you download data from another computer, always download to a floppy disk instead of to a hard disk. Then, before copying data from the floppy disk to the hard disk, use the DOS CHKDSK command to check for hidden files. To do this, enter chkdsk a:, where a is the drive that contains the floppy disk. If the disk has a label, you can expect one hidden file, but if the disk contains any other hidden files, DO NOT copy the data. Determine if the disk has a label by using the DIR command to ask for a directory of the disk: Enter dir a: at the DOS prompt. If the disk has no label, DOS will report Volume in drive A has no label.

* Periodically, use the CHKDSK command to check your DOS directory. In particular, watch for a change in the number of hidden files. An original DOS disk will contain two hidden files (IBMBIO.COM and IBMDOS.COM) or three if the disk has a label.

* To help detect a virus in your files, maintain an up-to-date hard copy of your directories and their contents. Use the DOS TREE command to print the directory structure. Likewise, use the DOS DIR command to print complete information about each subdirectory's contents. Watch for any inexplicable changes in file size and for the appearance of new files.

* Use the DOS SORT command or a DOS utility such as Directory Assistance (Individual Software, Belmont, Calif.) or Hot (Executive Systems, Sherman Oaks, Calif.) to sort each of your subdirectories by date and time. Any date before 01/01/80 should be suspected. Dates in the future should be carefully checked, as should any date that contains 00 or any time later than 23:59:59.

* Sort each subdirectory by file size. Be alert for unusually large files or files with a size of 0 bytes. Compare file sizes with your hard copy: Any inexplicable size change in COM, EXE, BAT, or SYS files should raise a warning flag.

* Sort each subdirectory by file name. If one of your files is called 123.EXE, for example, and you find a file with the same name but the file extension .COM, this could spell serious trouble. A COM file executes first in the DOS hierarchy. Also, look for file names that seem odd according to your naming conventions.

* Sort each subdirectory by file extension. You may not have picked up suspicious-looking files or extensions--such as DBASE.EVL or 123.WK8--the first time through.

* When recycling a floppy disk, always use the DOS FORMAT command to reformat the disk; DO NOT simply erase all the files from the disk.

* If you're serious about virus prevention, prepare a "clean boot" disk. To do so, turn off your PC, insert an original DOS disk in drive A, and turn the PC back on. Enter diskcopy a: a: at the DOS prompt and follow any further screen prompts. Henceforth, use this duplicate to start up your system.

* Prepare another clean disk containing at least your DOS files. Include any other files a virus writer might expect to be on a disk--CONFIG.SYS, AUTOEXEC.BAT, and 123.EXE are good candidates. Write-protect this disk. Then if you need one, you'll have a reliable backup of these files.

* If you find any suspicious files, remove them with one of the previously mentioned utilities. The idea is to eradicate them completely. Do not use the DOS DEL command, which merely replaces the first letter of the file name so that it won't show up when you execute a DIR command. Any file deleted with the DEL command continues to exist until it is overwritten. Likewise, do not use the DOS ERASE command.

Source Citation
Kane, Pamela. "Protecting against computer viruses; know your enemy." Lotus 4.7 (1988): 17+. Computer Database. Web. 31 Jan. 2010. .

Gale Document Number:A6810415

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