Gusto raises $140M, Xero acquires Hubdoc, why the IRS should allow taxpayers to use U2F keys, and the open office under attack

Summary: The Government Accountability Office (GAO) has recommended the use of phishing-proof FIDO security keys to prevent tax scams. Also this week: payroll and HR provider Gusto raised a $140 million Series C at a $2 billion valuation; cloud accounting software maker Xero has moved to acquire Hubdoc (a data capture solution); Stampli, an invoice management platform for midsize and enterprise businesses, raised a $6.7 million Series A; and attacks on the open office continue unabated.