DOS Days

Frisk Software International


The company name, a combination of the founder's firstname and surname, Fridrik Skulason, is probably not one you would remember, but their product, F-PROT, was a staple anti-virus utility back in the DOS era. It was made popular largely because for non-commercial private use, it was completely free to use. The Rekjavik, Iceland-based company started around 1995 with F-PROT as their core product, though Fridrik's anti-virus program actually started life back in 1990 and was sold as shareware.

The FRISK Software International website back in 2005

F-PROT typically has 3 files that make up the virus definitions ("signatures"), which are:

  • SIGN.DEF - DOS and Windows virus search/disinfection data
  • SIGN2.DEF - Trojan, Java/scripting/BAT and other virus search data
  • MACRO.DEF - Word and Excel macro virus search/disinfection data

The first releases of F-PROT were the sole work of its author, Fridrik Skulason from Reykjavik, Iceland, with no company name. It was sold as a commercial product in Iceland but was released as shareware - for single users it was free to use with a small fee per machine for commercial and educational institutions.

F-PROT version 1.13 was released sometime in late 1990. It was able to detect and remove 11 viruses.

F-PROT version 1.14 was released on 21st January 1991. It claimed to be able to detect and remove 157 "families" of viruses and 250-300 "variants". It also had some support to check for unknown viruses. All programs were command-line utilities only - there was no front end. It came with an installable memory-resident driver, F-DRIVER.SYS, that protected you from file and boot sector viruses, and only used about 2300 bytes of memory. If you didn't install this you could still run a check for viruses in memory using F-SYSCHK. F-LOCK and F-POPUP were two memory-resident programs designed to check for trojans. They took up about 4 KB of memory.

From F-PROT version 2 and beyond, the product became a more cohesive program rather than a collection of anti-virus utilities. Many of the previous utilities were combined into one.

F-PROT version 2.02 was released on 7th February 1992. It added detection and removal of 72 more viruses over the previous release, as well as detection only for a further 33. It came with a much faster 'Secure Scan', and the 'Analysis' mode became an option under 'Secure Scan' rather than being on its own. You could also now run a scan that included file, boot sector, trojan, and user-defined patterns with a single command. VIRSTOP.EXE replaced F-DRIVER.SYS and F-NET.SYS (previously used if you had a Novell Netware network) as the memory-resident portion of F-PROT.

F-Prot v2.02 in action

F-PROT Professional for Windows was first launched in 1993 by FRISK Software International's OEM partners Data Fellows (now F-Secure) and Command Software Systems.

F-PROT version 2.11 arrived in February 1994, providing a revised installation menu and detection and removal of a further 401 viruses plus detection of an additional 51 viruses that destroy files (these viruses cannot be removed). This brought the total number of detected viruses up to 3,356. The virus naming convention now follows CARO syntax.

F-PROT version 2.14 arrived on 15th September 1994, adding detection and removal of 179 new viruses plus detection of an additional 37 viruses that destroy files (these viruses cannot be removed). This brought the total number of detected viruses up to 4,460.

F-PROT version 2.24a arrived on 20th August 1996, with detection of 8,427 viruses with safe removal of 6,219 of them. It continued to add to the growing list of Word and Excel macro viruses with its F-MACRO Windows program that first arrived in v2.23. Version 2.24a can now send you an email when new virus definitions are available.

F-PROT version 2.27 arrived on 27th May 1997, with detection of a further 600 Word and Excel macro viruses.

F-PROT version 2.27a was released on 22nd July 1997, and would be the final version 2.x produced as version 3 was now just about ready.


F-PROT Version 3.00 arrived in April 1998 and gave us a different user interface that kept option selections quick and simple, and also made use of a DOS extender to allow the use of extended memory (XMS). This version also combined the previous F-MACROW and F-PROT into a single program.

F-PROT version 3.11 was released in September 2001.It could detect over 57,900 viruses and trojans. Most updates to the actual anti-virus software were now being made to the Windows version, so only minor updates could be seen in DOS versions. The virus definition files were now just over 1.2 MB in size.

F-PROT version 3.16a was made available for download in December 2004, with the last virus definitions on this version dated 9th February 2005. For DOS and Windows these definitions could detect 56,443 viruses and 56,082 trojans. In addition, it could detect 8,418 viruses for Word/Excel, 6,463 script viruses, 3,377 BAT file viruses, and much more.

F-PROT version 3.16b was made available for download in March 2005.

Version 3.16c was released in June 2006. It supported scanning inside .ARJ, .CAB, .LZH, .ZIP, and .RAR archive files (v2.5 and older only)

Version 3.16f of F-PROT anti-virus software for DOS is a complete monitor, scanner and disinfectant. This version has the latest definitions up to 8th January 2009 with over 311,000 virus definitions stored. It definitely wins the 'numbers game' claiming it can detect over 434,376 DOS/Windows viruses and 158,607 trojans, 44,232 scripting language viruses, 8,755 Word/Excel macro viruses, 698 Java viruses, 5,246 BAT viruses, 3,334 IRC INI file viruses, 605 IS INF file viruses, 687 UNIX shell script viruses, 248 PHP viruses, 620 UNIX file viruses, and over 15,750 others through generic means.


It can scan within archives (ARJ / CAB / LZH / RAR / ZIP), many packed executables and emails. Running it today requires the use of the /OLD command-line argument to ignore the fact that all .DEF (virus definition) files are out of date.

The F-PROT program comprises the following tools:-

F-PROT.EXE is the scanner which can run either as a standalone DOS application or via command-line arguments.
F-FCHK.EXE can be used to check individual files for infection.

F-Prot in Modern Times

The F-Prot AntiVirus for Windows product is still around today! (2023), though since 2012 has been a part of the Cyren company after its acquisition by Commtouch. FRISK’s founder, Friðrik Skúlason, joined Commtouch as vice president of antivirus technologies. F-PROT was declared end of life on July 31st 2021, so is no longer being maintained as a separate product.