Virtually any media that can carry computer data can carry a virus. Computer viruses are usually spread by data diskettes, but can be downloaded from the Internet, private bulletin boards, or over a local area network. This makes it extremely easy for a virus to spread once it has infected a system. This is an extremely rare occurrence, as most software companies go to great lengths to provide clean software. There is a huge commercial interest in keeping computers virus-free.
Companies stand to lose literally thousands of dollars if they lose computer data to a virus.
An immense amount of time can be lost from more productive endeavors if someone has to check or clean each computer and floppy diskette of the virus because, no matter what, it will continue to replicate itself until it uses every bit of memory available. To service this market, companies sell anti- virus software, which scans programs, searching for viruses. If one is found, a user can kill it by cleaning the file, delete the file itself, move the file to a disk, or ignore it. Ignoring a possible virus is an option provided because some of the newer software utilizes heuristic algorithms to detect possible viruses. This method of detection is highly effective but, because of the sensitivity of the programs, false hits can occur.