The Universities Superannuation Scheme is a UK pension scheme for universities and other higher education institutions.
The company has paid 97 pence per share, reflecting a 34% premium to KCOM's closing price of 72.5 pence on Tuesday.
Shares in KCOM Group immediately jumped up by 34% on Wednesday afternoon.
"The board believes that USSL's offer for KCOM provides, on completion, both meaningful, guaranteed cash returns for shareholders as well as a strong, supportive partner in our endeavours to take the business forward to new successes," said Interim Chair Patrick De Smedt.
"The board believes that the offer of 97p per share represents a compelling opportunity for shareholders to realise an attractive cash value in respect of their shares and recognises the quality of KCOM's businesses and the strength of their future prospects. For all these reasons, the board unanimously recommends that shareholders accept the offer," Smedt added.
Arma Partners acted as financial advisor to the buyer, Humber Bidco.