About 30,000 customers of the Cheshire-based ISP Vispa were forced offline for almost 12 hours today by a DDOS attack traced to the Baltic state of Latvia.
Broadband service has now been restored, a spokesman said, but customers are unable to call customer service because the firm's phone system was also crippled by the attack.
"As a result of a major denial of service attack on our network we suffered a severe outage between 1am and 12.30pm Friday January 8," Vispa commercial director Adam Binks said.
"All services have now been restored except for our phone system which has been affected as part of the problem. We are currently working with suppliers to have the main numbers diverted to other lines within the office but expect to restore the system by the end of today."
DDOS attacks on British ISPs apparently from inside former Soviet bloc countries are common, but it is rare for them to have such a paralysing effect.
Vispa apologised to customers for the outage and said it was "taking measures to prevent such an attack happening in the future". ®