What can I do if an ex-employee tries to create the same product and an identical company name as mine?

If an ex-employee of my company try's to create a nearly identical product with the same name, and nearly identical domain name, is there anything I can do? In 2005 I registered a domain name for the use of creating an online product, lets call this domain name "onlineproducts.com" and call the product "the product". Between then and 2008, several people began helping me on "the product" and we gained a sizable user base. Soon after I also purchased "abcs.org" and "abcs.net". In 2008 I registered a company in Delaware called "ABC LLC", to begin turning the site/product into something more serious. We also began working on "the product" version 2 (the same name as the original). Late last year, two of the key developers of v2 quit, and at that time the "abcs.org" expired. Now, the two key developers have bought "abcs.org", are continuing development of v2 under the same product name, and are calling their 'group' "ABCs". They are not a registered company, just a group of people. Neither "ABC" or "the product" are registered TMs, however we have been using them for over 5 years now.