MicroStrategy Inc (MSTR.O), a major bitcoin corporate backer, said on Tuesday it was offering $500 million in bonds and the proceeds will be used to buy bitcoins . This comes a day after the world"s largest publicly-traded business intelligence company said it planned to raise $400 million through senior secured notes due 2028 in a private offering. The company spent the last year steadily amassing more bitcoin after making its first investment in August as the cryptocurrency soared in value. It has since made multiple purchases of the digital currency. The senior secured notes offering, expected to close on June 14, will bear an annual interest rate of 6.125%, the company said. Bloomberg News first reported the news of MicroStrategy"s increased size of bond sale earlier in the day, citing a person familiar with the matter. Our Standards: The Thomson Reuters Trust Principles.