Guy’s and St Thomas’ NHS Foundation Trust has claimed it is recovering from a serious IT breakdown but with some systems still out of action.
There have also been reports that some systems were out of support earlier in the year.
A systems failure in late July led to the cancellation of appointments for some patients.
On 4 August, the trust had a statement on its website attributing the problems to the recent heatwave and confirming that some activities were still being postponed.
“We're working hard to fix these problems and are doing everything possible to minimise the impact this is having on our services,” it said.
But there have been indications that there were previously worries about security risks.
A report to the board of directors on 27 April stated that a number of IT systems, including Windows 10, were out of support and the infrastructure had reached the end of its life.
“Work had taken place over the last six months to partially mitigate the associated security risks through applying tactical fixes to the most serious areas of risk,” the document said.
“The committee noted that some areas of the trust remained vulnerable to a cyber attack and that it had seen a recent increase in targeted phishing attacks. Assurances were sought about how the data, technology and information team had confidence that all areas of risk had been identified and mitigated as far as possible.”
According to a report in the local newspaper Southwark News, the trust said it is planning to commission an independent external review on the details of the failures.
Responding to questions from UKAuthority, a spokesperson from Guy’s and St Thomas’ said: “Our core IT systems are now up and running, with further systems coming online every day. Work continues to recover and reconcile a large number of smaller applications and this is being done based on clinical priority.
“Whilst we have continued to deliver most of our services, and our staff are doing everything possible to minimise the impact on patients, regrettably we have had to postpone some operations and appointments. We are extremely sorry for any disruption and have apologised unreservedly.
"We are contacting these patients directly to rearrange their care at the earliest opportunity. We thank our staff for their dedication and resilience at this very difficult time.
“During the extreme heat on 19 July, the data centres at both Guy’s and St Thomas’ failed. The complexity of our current IT systems has made them very difficult to recover. In addition, we need to manage the move back from paper to digital in a safe and carefully planned way.”