O’Reilly Media’s 2015 Open Source convention (OScon) turned into a debacle on Twitter last week after the invitation of a controversial activist. The drama escalated after O’Reilly Media employed a flawed mass-blocking tool on its official Twitter accounts, which blocked a swathe of journalists and developers in addition to the convention’s critics.

The convention began receiving criticism after the decision to invite activist Randi Harper to give a talk on online harassment. Harper claims to be a campaigner against online abuse, but her role as an instigator of a number of online harassment campaigns has made her a a highly controversial figure, who many accuse of hypocrisy.

O’Reilly media’s social media manager Josh Simmons further inflamed the situation by installing “GGAutoblocker,” a mass-blocking tool developed by Harper, onto the convention’s official Twitter account. The tool has been criticised in the past for labeling a vast number of innocent Twitter users as “harassers.”

This criticism is supported by peer-reviewed research on the autoblocker, which found that just 0.66% of users blocked by the tool can be accused of genuine harassment. The autoblocker operates on the basis of guilt by association, with users automatically added to the blocklist based on who they follow.

After installing the tool on O’Reilly Media’s OScon Twitter account, tech journalists and developers began to report that they had been blocked.

O’Reilly Media is one of the world’s leading publishers of books on computing and technology. It is credited with popularizing a number of important terms in the world of technology, including “Open Source” and “Web 2.0.”

However, longtime customers of the company found themselves blocked on social media during the conference and took to Twitter to signal their discontent. One popular user pledged that his company would stop purchasing O’Reilly Media books in the future.

As the controversy escalated, the company’s community manager conceded that there were problems with Harper’s blocking tool and deactivated it.