The NHS has warned the appointments at hospitals and GP may be slower than normal while the disruption caused by the ransomware attack subsides.
"All GPs surgeries did open, though some of them had to use pen and paper", said Ms Rudd.
"The vast majority of patients have noticed no difference".
"This one, we knew it could be a problem", the official told Reuters.
But some other technology industry executives said privately that it reflected a widely held view in Silicon Valley that the USA government is too willing to jeopardize internet security in order to preserve offensive cyber capabilities.
The Health Secretary said the NHS had not suffered a feared second wave of attacks, as millions of NHS workers returned to work yesterday.
Some said they were left "angry and upset" at being turned away because records could not be accessed.
It said: 'There were no infected computers in North East GP practices and the priority through this global malware incident was to protect the NHS computer network, clinical systems and patient data - and this was done very successfully.More news: Am Tamil for 43 years, says Rajinikanth
She added: "The IT systems of a small number of GP practices across Tayside, which operate independently of NHS Tayside's systems, were affected, and our eHealth team are working with these practices to resolve this issue".
But these two hospitals were taken off of "divert" status on Tuesday afternoon - meaning patients can now attend all A&Es as normal.
"This is a wake-up call for the NHS but also more generally to businesses around the country".
In his first public comments since the attack on Friday, Mr Hunt told Sky News: "Although we have never seen anything on this scale when it comes to ransomware attacks, they are relatively common and there are things that you can do, that everyone can do, all of us can do, to protect ourselves against them".
"While Microsoft's release of back-ported patches is a commendable proactive action, the ACSC considers organisations running Windows XP, Server 2003 and other unsupported operating systems to be exposed to extreme risk", the organisation said in a statement.
NHS Digital has announced updated guidelines on protecting against future cyber-attacks including instructions to install a patch to protect systems against further attacks and malicious viruses.
NHS Digital said it had made health trusts aware last month of IT protection that could have prevented the damage.