SAN FRANCISCO — Hewlett-Packard Co. is churning through outside counsel as it confronts an avalanche of shareholder suits over its widely panned acquisition of Autonomy.

The embattled personal computer maker has tapped New York's Wachtell, Lipton, Rosen & Katz and San Francisco's Farella, Braun & Martel to defend it, ousting its newly hired lawyers at Morrison & Foerster, according to a substitution of counsel filed Tuesday in federal court. The team is the third in just more than a month to represent HP in securities actions stemming from its 2011 purchase of Autonomy, a British software maker. MoFo partners Darryl Rains, Judson Lobdell and Mark Foster entered the fray for HP in late June after the company ditched Morgan, Lewis & Bockius, a long-time favorite firm.