"Bitten by a Zombie? Become a pirate? Take the 80s music quiz? Some of them may be annoying but Facebook's applications have played a large part in the site's success.

The free plug-ins are created by amateur and professional software developers. They allow users to customise their personal pages.

Among the most popular are "Causes" which lets members to show their support for a campaign, "Hug me", a way of expressing electronic affection, and "Super Poke" which involves throwing sheep at other people.

Now a change in the way applications are promoted has caused a row. Facebook is offering to "verify" applications for a $375 (£250) annual fee.

After going through a testing process, successful apps will be given a badge, showing they meet certain standards. Verified applications will also receive heavier online promotion. "