The move by Symantec, which has fired two CEOs since 2012 as its stock and financial performance lagged many other software makers, follows a trend of companies splitting in an effort to boost their share prices. The deal also reverses its long troubled $13.5 billion acquisition a decade ago of storage software maker Veritas. Slowing PC sales have hurt its security sales, while sluggish demand for its storage and data management software has diminished the value of Veritas, which was seen as a “cash cow” when it was purchased.