The companies cite success stories of customers who have buried snippy blog comments, embarrassing photos or critical mentions of their names. But, as Ms. Parascandola found out, the services can’t wipe everything off the Internet, and their efforts can backfire. ReputationDefender sent a letter to political blog Positive Liberty asking it to remove Ms. Parascandola’s name from a critical entry on the grounds the post was “outdated and invasive.” Blogger Jason Kuznicki refused, and posted a new entry mocking the request. He says he “had a good laugh over it.”