People are being advised to pick up the telephone or visit the city council offices after their IT systems were hacked on Monday.
Staff and councillors are enduring their fourth day without use of their website or emails.
The city council's clerk said the hacking had been a 'sophisticated attempt' and that the council is awaiting a detailed report but had not contacted police.
He said: "Our website has been hacked and our technical advisers are on the case.
"It is beyond a nuisance. Pick up the telephone or come in. It is a major nuisance upon our business efficiency."
The clerk has said there is no evidence of data loss.
To contact the city council call 01243 788502 or visit the council offices in North Street.
Bognor Foodbank reveals 20 per cent rise in people fed
Read more at: https://www.chichester.co.uk/news/bognor-foodbank-reveals-20-per-cent-rise-in-people-fed-1-8624894