SAN FRANCISCO • Wikipedia has blocked more than 300 accounts used by people who are paid to create or tweak entries at the communally sourced online encyclopedia.

Weeks of investigation revealed that 381 accounts are being used on the English version of Wikipedia for "black hat" editing, in which people took money to promote outside interests without disclosing they were on someone's payroll, according to a Wikipedia blog post on Wednesday.

Wikipedia editors who led the investigation found reason to believe that some tactics used were malicious and might even be considered extortion.

In some cases, people pretending to represent Wikipedia reached out to subjects of articles seeking payment, according to the widely used online encyclopedia.

"Other times, these individuals would threaten to delete the article if the subjects of the article failed to make payment," Wikipedia told AFP. "That being said, we would agree that the actions taken by (those) behind these accounts were extortionate and even, in some cases, similar to blackmail."

Wikipedia is powered mostly by volunteers and bars paid advocacy that is not disclosed, such as in the case of museums or universities having employees tune entries related to exhibits or institutions.

"Neutrality is key to ensuring Wikipedia's quality," Mr Ed Erhart and Mr Juliet Barbara of the non-profit Wikimedia Foundation said in the blog post.

They added: "Although it does not happen often, undisclosed paid advocacy editing may represent a serious conflict of interest and could compromise the quality of content on Wikipedia."

The accounts identified during the investigation were used from the end of April to early August, but the nature and quality of edits suggested that the paid scheme was operating "for some time" before being discovered, according to Wikipedia. More entries may be removed as the investigation continues.

AGENCE FRANCE-PRESSE