SCO has announced that it has obtained more payments from firms using Linux.
DaimlerChrysler is being sued by SCO
It said that software giant Computer Associates, plus Questar and Leggett & Platt, have paid it to use code that SCO claims has been illegally included in Linux.
The US firm has also taken legal action against DaimlerChrysler for its use of the open source operating system.
The legal action against the car maker is the second suit launched against companies using the popular software.
The news caps a busy week for SCO during which it announced that car parts firm AutoZone was the first end user to be sued.
Technology news site CNet revealed that early versions of SCO documents showed that it was originally planning to sue the Bank of America.
This week also saw EV1 Servers become the first firm to go public with the news that it had paid SCO to use some of its intellectual property.
SCO claims that computer code it owns has been illegally included in recent versions of the Linux operating system.
It started a $5bn lawsuit against IBM accusing the computer giant of putting this code into Linux.
This week a US Judge ordered both IBM and SCO to disclose more information about the disputed code.
IBM has been told to make public all the contributions it has made to Linux and SCO must provide more detailed information about what it believes IBM has done.
So far SCO has only obtained $20,000 in licence payments
The payments by the four companies are widely being seen as insurance policies to head off the threat of legal action later on.
Computer Associates said its payment was made as a settlement with another company and was not made as a result of SCO's licencing program.
It added that it did not approve of SCO's methods.
SCO is seeking payments from those running Linux for use of this disputed code.
Financial results announced by SCO this week show how the legal action is affecting its bottom line.
During the quarter ending on 31 January SCO lost $2.25m. During the same period last year it lost only $724,000.
Much of the loss was blamed on the legal costs.
By contrast SCO has only won $20,000 in licence payments for its disputed intellectual property.
Many people in the open source movement dispute SCO's ownership of the code in question.
The fact that SCO has declined to make public which parts of Linux it claims to own has fuelled scepticism in the open source movement.
Those who oversee the kernel, or core, of Linux have offered to remove any parts of it that have been illegally included. But, so far, SCO has not taken up this offer.
Doubts about SCO's claims have also been raised by websites that specialise in the history of Unix and other operating systems.
They have dissected some of the components SCO is known to be claiming as its own, showing where they came from and how widely they are used.
SCO is being forced to go to court to defend its claim on this computer code.
In an ironic twist to the whole saga, server monitoring firm Netcraft has revealed that the US District Court in Nevada, where SCO filed its lawsuit against Autozone, uses Linux software to run its web server.
Questions were also raised about Microsoft's involvement in the saga.
Open source guru Eric Raymond revealed an e-mail which he claimed showed Microsoft was investing in SCO.
SCO disputed the claim and said the consultant who wrote the message was mistaken about Microsoft's involvement with SCO.