The Wikimedia Foundation, the organization behind omnipresent online encyclopedia Wikipedia, has revealed that almost 400 user accounts have been blocked by volunteer editors.

The accounts in question relate to “undisclosed paid advocacy” — people who were paid to promote a certain agenda in Wikipedia articles. In addition to removing 381 accounts, editors also ditched 210 articles created from scratch by these accounts.

It can be difficult to pinpoint when an article has been created by so-called “sockpuppets,” but by looking at edits made across a number of articles, it’s possible to identify patterns and make some assertions.

“Most of these articles, which were related to businesses, business people, or artists, were generally promotional in nature, and often included biased or skewed information, unattributed material, and potential copyright violations,” Wikimedia said in a blog post. “The edits made by the sockpuppets are similar enough that the community believes they were perpetrated by one coordinated group.”

Wikimedia’s terms of use specifically prohibit:

…engaging in deceptive activities, including misrepresentation of affiliation, impersonation, and fraud. As part of these obligations, you must disclose your employer, client, and affiliation with respect to any contribution for which you receive, or expect to receive, compensation.

However, it’s worth noting here that not all paid editing contravenes Wikipedia rules — some PR firms have signed an agreement with the Wikimedia Foundation that assert they will adhere to the paid-editing guidelines, while other public organizations such as universities have employees that update information on the encyclopedia. Disclosure is key.

Wikipedia has a long history of black-hat editing, dating back to its beginnings. Perhaps the most high-profile case in recent times came back in 2013, when the Wikimedia Foundation sent a cease-and-desist to Wiki-PR, an agency set up specifically for paid edits. Around 300 accounts were shuttered as a result of that case.