A Cabinet Office spokesman said later: "The amendments made to Wikipedia are sickening. The behaviour is in complete contravention of the Civil Service Code. It is entirely unacceptable.
"This investigation is being led by the Cabinet Office permanent secretary, Richard Heaton, who is responsible for the Government computer network. He will be working closely with the director general for propriety and ethics and her team, as well as other senior officials.
"We are treating this matter with the utmost seriousness. Our first priority is to establish the facts and to examine the issues raised. Once we have the facts, we will update Parliament with the findings and consider further appropriate action.
We will be keeping important stakeholders including the Hillsborough Family Support Group, the Hillsborough Justice Campaign, the Rt Rev James Jones, and the All Party Parliamentary Group on the Hillsborough Disaster updated.
"In addition we will invite the Rt Hon Andy Burnham MP, who has a deserved status as an expert on the disaster, to view all relevant material from the very outset and at every stage so that he can assure himself that all steps have been taken.
"At this time, we have no reason to suspect that the Hillsborough edits involve any particular department, nor more than one or two individuals in 2009 and 2012.
As the first incident happened five years ago and there are hundreds of thousands of people on the Government's network, it may prove challenging to identify who was involved. But we are exhausting every option. Anyone with information should contact the Cabinet Office.
"No one should be in any doubt of the Government's position regarding the Hillsborough disaster and its support for the families of the 96 victims and all those affected by the tragedy."
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Cold with further wintry showers Friday night, then turning icy. Some sunshine, especially on Sunday - but sleet, snow & ice Saturday night
Detectives have released CCTV footage of the moment a machete wielding thug wearing a mask jumped over the counter at a bookmakers.
A cold wind. A strong wind. Icy and wintry into the weekend