Symantec Corp. shares jumped more than 17% at times in Tuesday trading, amid a report that the security-software company has been approached by a private equity firm. Reuters reported that Thoma Bravo has expressed interest in acquiring the company known for its Norton antivirus program, which refocused more on corporate security after acquiring Blue Coat Systems from a different private-equity firm. Symantec stock has already enjoyed gains in the past week, after its quarterly earnings report sent shares higher on hopes for the enterprise-security business.