According to David Harley, research author with Eset (company that specializes in providing security software solutions), there are older viruses out there that can still infect your PC. The infection may get onto your computer before you get to install security software, or even worse, because your up to date antivirus does not detect it. The virus is so old that the manufacturer will not include it in the software and consequently the virus goes undetected.

Take the Stoned.Angelina virus, for example, which was discovered in January 1994 by Symantec and is still in the wild. This virus works by infecting the DOS boot sector of floppy disks and by infecting the MBR (short for master boot sector) of your HDD. In order to get infected with the Stoned.Angelina all you had to do was leave an infected disk in the floppy drive and reboot your system.

How can you still get infected with such a virus nowadays? This is the first case scenario: let's say that you format and reinstall the operating system, but forget to take out the infected disk. By the time you get to install a security software, you are already infected. The simplest way to prevent this from happening is to reconfigure the CMOS setting so that the PC's first boot device would be the HDD, not the floppy. This way the computer would boot directly off the HDD and it wouldn't matter if the floppy disk was infected or not.

There is another way that an antique virus can get onto your system. Antivirus software companies have to maintain a competitive product and in order to do so they sometimes disregard older viruses. The simple truth of the matter is that by dropping a few really old virus zoos the software will perform better. In regard to the Stoned.Angelina virus it was considered obsolete and thus detection for it was dropped.