The fake statement claimed that the company had recorded expenses that did not comply with accounting standards. It also said that the firm fired its CEO.
G4S confirmed that the release was fraudulent.
"We have been made aware of a fraudulent website and news release purporting to be from G4S which has been released to members of the media this afternoon," the company said on its website. "The website and the announcement contain wholly inaccurate information."
If the purpose of the email was to affect the company's share price, it wasn't successful. Stock lost some gains immediately after the statement was received, but quickly recovered to trade 2.3 percent higher.
"Media relations manager" Piers Zangana was given as the contact at the bottom of the email - but he left the company last month, according to his Linkedin page.