The bot that reverts edits adding links to blacklisted or frequently abused websites is XLinkBot.
XLinkBot is an approved English Wikipedia bot operated by human maintainers and designed to make repetitive anti-link-spam edits. It compares edits against a configurable revert list and can undo additions made by new or anonymous users when a matching domain or pattern appears. Established users may be treated differently, and administrators can adjust the bot’s settings and lists.
The bot began its wiki life as SquelchBot and later took up work associated with AntiSpamBot. Its code and operations were developed to handle recurring external-link abuse, and it is intended to run continuously when hardware and network conditions permit.
A useful distinction is that XLinkBot is not the same thing as Wikipedia’s MediaWiki:Spam-blacklist. The blacklist is a site-wide mechanism for domains that are inappropriate, while XLinkBot’s revert list can act as an intermediate measure for domains that may have legitimate uses but are repeatedly misused. The bot can occasionally revert an appropriate link, so editors are told to review the edit rather than trust automation blindly.