Following a series of high-profile attacks that leveraged security vulnerabilities in its PDF Reader and Acrobat applications, Adobe Systems Inc. is making a major push to revamp its approach to security. The company said today that it plans to ship security updates more regularly and push out emergency updates more speedily, and that it will be continually stress-testing those products to find and close security holes before hackers can exploit them. In announcing the changes, Adobe is borrowing several pages from Microsoft’s security playbook. Redmond ships updates on the second Tuesday of each month and regularly fixes vulnerabilities that its in-house researchers have uncovered. Sometime this summer, Adobe will begin shipping patches on a quarterly basis — on the second Tuesday of every third month. Brad Arkin, Adobe’s director for product security and privacy, said that day was picked to help lighten the load on businesses, most of which already