Microsoft wants the US Senate to rewrite anti-spyware legislation in order to protect companies that provide spyware removal utilities.

The software maker warned on Tuesday two bills approved by the House of Representatives this week fail to prevent "frivolous lawsuits" filed by adware and spyware companies that are upset when their code is removed.

"These bills leave companies that are responding to consumer demand for strong anti-spyware tools vulnerable to frivolous lawsuits brought by the very companies responsible for the proliferation of spyware and other deceptive software," Jack Krumholtz, the head of Microsoft's lobbying office, said in a statement. Microsoft began offering a spyware removal utility this year.

Microsoft's fears are hardly theoretical. Gator, now known as Claria, sued anti-spyware company PC Pitstop on grounds that included trade libel, false advertising and tortious interference. Claria distributes pop-up ad software, often bundled with free applications, that some surveys say is installed without a person's direct knowledge and consent.

New.net sued Lavasoft -- maker of Ad-Aware -- in federal court. And spyware researcher Ben Edelman has indicated that he has received threats from Claria and WhenU.

In January, Microsoft introduced a beta of its Windows AntiSpyware application, which is currently available at no cost.

The Senate is considering what to do with the spyware legislation but is not close to finalising anything. Microsoft's Krumholtz said: "We are hopeful that the Senate will include in its bill a provision to prevent those who traffic in spyware from suing companies like Microsoft to keep them from providing these valuable consumer protections."