The Department of Homeland Security wants to know the identity of one of its anonymous critics, and Twitter today filed a lawsuit to prevent the agency from finding out.Twitter said in a Thursday filing that it seeks to prevent US Customs and Border Protection (a DHS agency) from "unlawfully abusing a limited-purpose investigatory tool to try to unmask the real identity of the operator of the @ALT_USCIS account. Since Donald Trump was inaugurated as president, many "alt"-government agency Twitter accounts—@AltStateDpt, @Alt_NASA, and so on—have emerged, either claiming to be operated by anti-Trump government staffers or anti-Trump activists."The Defendants are now threatening the anonymity of the person(s) speaking through the @ALT_USCIS account," Twitter's lawsuit states. "Specifically, on March 14, 2017, they issued and delivered to Twitter an administrative summons (the "CBP Summons") demanding that Twitter provide them records that would unmask, or likely lead to unmasking, the identity of the person(s) responsible for the @ALT_USCIS account."Continue reading on VICE News.