Apple has laid legal claim to the word "Pod", arguing that other companies that use the word as part of their product names risk infringing the trademark of its popular iPod music player.

The legal campaign, which in recent days has drawn challenges to products with names such as Profit Pod and TightPod, reflects a broader attempt by some of the most successful consumer technology companies to prevent their best-known product names slipping into common usage beyond their control.

This month, Google drew attention to its own long-running battle to defend the trademark in its name when it wrote to the Washington Post to protest at the use of the verb "to google", though examples of similar warning letters date back at least four years.

Lawyers acting for Apple have in recent days written to at least two companies that use the word "Pod" asking them to drop the word from their product names, though the wider extent of the legal challenge remains unclear.

Dave Ellison, whose company, Mach5Products, makes the Profit Pod, said he had been sent a "cease and desist" request by Apple's lawyers last week, just after receiving trademark recognition for his product name in the US. In the letter, Apple's lawyer said the name of the handheld device - an infrared scanner used to record activity on arcade video game machines - was based on a "a Pod-formative mark and incorporates a substantial portion of Apple's iPod mark".