Hacks follow those on Bouygues and Zaha Hadid
Interserve and Bam are the latest firms to have suffered cyber security attacks.
A spokesperson for Bam said the business had held up well against a “a significant cyber attack" that was part of a wave on public and private organisations involved with helping battle covid-19.
He said: “Supplier and employee payments are being made and so it is, for our clients, subcontractors and our teams, pretty much business as usual."
The firm, which is due to build another Nightingale hospital in Exeter, said its IT teams had closed access to a number of systems, including its website, as a precaution and had alternative arrangements in place to ensure business continuity.
The spokesperson added: “Our own precautions have had more of an effect on our normal working procedures than the virus itself but it is important for us to be absolutely confident that restoring all systems – at a time when we are working from home in unprecedented numbers – is done carefully.
“We have reported the attack to the authorities and, as everyone would after such an event, are taking the opportunity to learn from it to make any necessary changes to our systems for the future.”
A spokesperson for Interserve, which was behind the Nightingale hospital in Birmingham, confirmed it was a target of a cyber security attack earlier this month.
He said: "Interserve is working closely with the National Cyber Security Centre and Strategic Incident Response teams to investigate, contain and remedy the situation.
"This will take some time and some operational services may be affected. Interserve has informed the Information Commissioner of the incident. We will provide further updates when appropriate."
Interserve’s employees, former employees, clients and suppliers have been asked to exercise heightened vigilance during this time.