Adware maker 180solutions claims to be a key witness in the case against three Dutchmen accused of running a botnet which controlled 1.5m PCs.

The group allegedly used the largest zombie army ever created to retaliate with a distributed denial of service (DDoS) attack against 180solutions after the vendor terminated its distribution contract.

180solutions develops an application called the Zango Search Assistant which offers access to games and premium content.

The application also comes bundled with software that presents pop-up ads as users surf the web. Many spyware detection and removal tools label the application as spyware, including Computer Associates' eTrust PestPatrol AntiSpyware.

Software distributors are paid a fee for every copy of the software they get installed, creating an incentive for botnet operators to install the software on hacked systems.

Industry experts claim that affiliates are paid between seven and 50 cents per installation.

180solutions has been trying to rid itself of the spyware image in recent months. In August the company filed a lawsuit against seven distributors which installed its software on botnets. The company now periodically notifies users that the software is present on their system.

Following the termination of his contract, one of the Dutchman is alleged to have started threatening the vendor and launched a DDoS attack against some of its websites. The attacks allegedly stopped after 180solutions agreed to pay a ransom.

The software vendor reported the attack to the FBI, resulting in the arrest of the three men in October.

The trio are charged with computer hacking, destroying automated networks, and installing adware and spyware. Authorities are still investigating their involvement in additional crimes including identity theft.