The sites were all defaced with a single, one-line message, offering a rude epithet and claiming credit for the Red Eye Crew, a Brazilian hacker group.
A number of the sites were pulled down following the hack, and several of them stayed down for more than a day, according to news reports.
The hacks have been tied to servers maintained by GovTrends, which oversees the maintenance of about 100 member sites and is one of a few outside technological specialists approved by the House's Chief Administrative Officer (CAO).
Last August, at least 18 Congressional member sites managed by the same vendor were defaced by Indonesian cracker 3n_byt3. That attack reportedly took place through a default login to the administrative portion of the sites, according to GovTrends.
The Red Eye Crew is a well-known hacker organization, with thousands of site defacements to its credit, according to reports.
In a letter, House Speaker Nancy Pelosi requested a full investigation of the hacks by the CAO:
"We request that you initiate an immediate and comprehensive assessment of how hackers were able to deface the websites of nearly fifty House Members and Committees last night.
"In the past, we jointly requested that your office review and tighten cybersecurity protections designed to ensure that congressional offices and committees are safeguarded from unauthorized intrusions. We appreciate the efforts you and your cybersecurity team have taken to tighten firewalls, as well as more recent efforts to ensure that official mobile communications devices are secure from hacking and other intrusions.
"However, last night's actions indicate that further review of security procedures are needed. From initial reports, these intrusions appear to be related to one website vendor which has had previous security failures. While many Members have expressed satisfaction with the vendor in question, this is the second time in a year websites hosted and supported by this vendor have been compromised."
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