A bipartisan group of senators is questioning eight major U.S. corporations about the transmission of American user data to foreign bidders, used for digital advertising in the majority of cases. “We write to seek information about your company’s sharing of Americans’ personal data in order to understand how that information may be obtained and exploited by foreign governments to the detriment of our national security,” the letter (pdf) reads. It was sent on Thursday by Senator Ron Wyden (D-Ore.) to the companies, seeking information specifically about the “real-time bidding” process, which refers to the milliseconds before ads are shown to people on their electronic devices when hundreds of companies participate in an auction for their advertisement to be displayed. “Few Americans realize that some auction participants are siphoning off and storing ‘bidstream’ data to compile exhaustive dossiers about them. In turn, these dossiers are being openly sold to anyone with …