Services by the Hull-based Kcom's group Karoo division were hit at around 11pm.
A Karoo spokesperson said: "We would like to apologise to customers who experienced difficulties accessing Karoo services for a short period last night.
"This was due to essential maintenance that was carried out for approximately 60 minutes.
"We are committed to a programme of improvements to our Internet infrastructure to ensure that our service is reliable and efficient.
"Customers can check the status of our service by visiting www.karoo.co.uk"