Security vendors have pledged support for antivirus firm Kaspersky in its US district court battle against software firm Zango.

The two companies are in court to decide whether Kaspersky is acting illegally in blocking Zango's ad-displaying software.

Zango offers access to multimedia files, games and utilities in exchange for agreeing to install adware.

The vendor argues that its products should not be considered adware because users are clearly informed about the ad-serving software before installing, and that all users agree to a Zango end user license agreement.

Zango was fined by the Federal Trade Commission in 2006 for using deceptive practices to spread its software.

The company has since changed its distribution policies and affiliate programme, and now claims to be completely in line with the requirements of the settlement.

However, critics still argue that the agreements are deceptively formatted and that Zango and its affiliates do not clearly define the software's function.

Other critics contend that users would not agree to install Zango if they were informed about the full results of an install.

Security vendors including McAfee and Sunbelt Software, as well as the Electronic Frontier Foundation, filed an Amicus Brief on Monday in support of Kaspersky.

The group claims in the filing that Kaspersky is protected from legal action by Section 230 of the Telecommunications Act 1996, which shields service providers and companies which filter indecent or unwanted content.

"When Congress enacted Section 230, it articulated and pursued three distinct legislative goals," reads the filing.

"In its brief, appellant Zango only emphasises one of the three goals, and Zango ignores the goal most relevant here, which is 'to encourage the development of technologies which maximise user control over what information is received'."

A spokesperson for Zango declined to comment on the filing, but directed vnunet.com to an earlier Amicus Brief filed in support of the company by the National Business Coalition on E-commerce & Privacy.

This filing argues that extending Section 230 protection to Kaspersky would set a dangerous precedent and put too much power in the hands of security vendors.

"It will effectively empower security software purveyors as the ultimate arbiters of 'objectionable' content on the internet," read the filing.

"This will endanger many legitimate applications, programs, content and online platforms."