The first microcomputer virus to appear in the wild, i.e. outside the single computer or lab where it was created, is celebrating its 25th birthday.

'Elk Cloner' was created in 1982 and is credited to Richard Skrenta, a high-school student from Pittsburgh.

The virus was originally added to a game propagated between Apple II computers via floppy disk. The game was set to play normally 49 times, but to release the virus on the 50th time of starting the game.

'Elk Cloner' would display a blank screen with a poem about the virus which read as follows:

It will get on all your disks.
It will infiltrate your chips.
Yes it's Cloner!
It will stick to you like glue.
It will modify RAM too.
Send in the Cloner!

The virus was originally developed as a joke, but it set the theme for a stream of annoying pieces of malware which popped up on the screens of Apple II, BBC Micro and, later, early PC users' screens.

"Back then it was just a prank, a bit of fun. Today's malware is frequently malevolent and coded by criminals and/or hackers," said Phil Higgins, a senior partner at secure networking firm Brookcourt Solutions. 

"These people are intent on extracting money from, and destroying the data of, innocent computer users and the organisations they work for.

"It is always nice to remember an anniversary, but this is one date that business and PC users should use to galvanise themselves into raising the bar on information security and ensuring that malware does not get through their security screens."

Although considered by most to be the first virus spread on microcomputers, 'Elk Cloner' was not the first virus ever created.

The first ever malware can be traced back to the early 1970s or even the late 1960s when programs called 'the rabbit' periodically appeared on mainframe computers.

Usually created as a prank by students, these programs cloned themselves and occupied system resources, thus lowering the productivity of the system.

There are also tales of a virus called 'Pervading Animal' which appeared in 1975 on the Univax 1108 system. This virus merged itself to the end of executable files, in much the same way as many modern viruses.