A San Francisco Bay area subscriber to Comcast Corp.’s high-speed Internet service has sued the company, alleging it engages in unfair business practices by interfering with subscribers’ file sharing. The subscriber based his claims on the results of an investigation by the Associated Press published last month that showed Philadelphia-based Comcast actively interferes with attempts some high-speed Internet subscribers to share files online. Mark N. Todzo, the lead lawyer in the case, said his client suspected before reading the AP report that Comcast was interfering with his Internet traffic. “What the AP report did was just confirm to him that it wasn’t just him who was suffering from the problem,” Todzo said. “There was this confluence of events where everyone seemed to reach the same conclusion, which was that Comcast was engaging in this activity.”