Homeowners and buyers have spoken of their “serious stress” after a cyber-attack played havoc with property completions.
CTS, which provides IT services to law firms, said systems were still not back to normal after more than three weeks of disruption.
Conveyancers have found workarounds that have allowed many people to go ahead with purchases.
But the scale of the problems has still not been revealed by CTS.
The company said it was “working around the clock” to restore systems, and had made “significant progress”.
“This is a very complex situation and, at this time, our focus remains on restoring those clients whose systems have been disrupted,” it said.
“We are keeping our clients updated and are in contact with the regulators.”
However, individuals whose home moves and mortgage completions have been affected by law firms’ inability to access documents said they were frustrated at the lack of communication.
One 33-year-old, who is buying a first home with his partner, said there had been few updates, and the last few weeks had been “seriously stressful”.
He said he was still concerned about whether all his personal details were safe.
Generally, on property completion day, the buyer’s solicitor arranges for money to be transferred to the seller’s solicitor. A failure to complete is technically a breach of contract.
The problem at CTS is having a knock-on effect on the firms involved in property completions.
Another homeowner affected, who did not want to be named, said he had been temporarily forced on to a more expensive variable rate mortgage because his new loan was unable to complete on time.
He and others have faced extra costs, but remain unclear about where to go for compensation.
The Solicitors Regulation Authority (SRA), which regulates law firms that carry out conveyancing, said anyone with complaints should initially contact their law firm. It is likely that these firms, in turn, may seek their own compensation from CTS or its insurers.
A spokesman for the SRA said a growing number of firms had informed the regulator about having been affected.
But he said that law firms had regularly been advised to ensure alternative options were in place should cyber-incidents occur.
A spokesman for the Information Commissioner’s Office (ICO), which regulates CTS, said: “People have the right to expect that organisations will handle their personal information securely and responsibly. If an individual has concerns about how their data has been handled, they should raise it with the organisation first, then report them to us if they are not satisfied with the response.”
He said CTS had told the ICO about the incident and the regulator would be “making enquiries”.