McAfee and Symantec are to sue software pirates who are selling counterfeit copies of their anti-virus software on eBay.
The action comes as part of a wider anti-piracy initiative launched by the US Software & Information Industry Association (SIIA) this week.
The SIAA is buying copies of software from eBay sellers to discover whether it is illegal or not.
Those found to be selling such goods risk lawsuits for damages. McAfee and Symantec are now involved in three actions against individuals, who allegedly sold thousands of items of pirated software in the last quarter of 2005.
Ebay says it is the responsibility of trademark holders to protect their brands, despite widespread theft often being conducted across its selling infrastructure.
Ebay claims it takes down all items found to be counterfeit, although it can not know this for sure unless it actually buys suspect items to inspect them.