Stocks finished on a strong note Friday, with the S&P 500 Index (^GSPC -0.16%) logging its fourth gain in the last five days, ending at all-time highs. But the success enjoyed by the wider market was a slap in the face for investors in Cliffs Natural Resources (CLF 0.89%), United States Steel Corp (X -1.00%), and Juniper Networks (JNPR 0.73%), which ended as the three worst performers in the S&P today. The benchmark index, for its part, added three points, or 0.2%, to end at 1,923.

Iron ore and metallurgical coal producer Cliffs Natural Resources lost 5.5% Thursday, ending as the day's most egregious decliner. The company's pugnacious quarrels with activist investor Casablanca Capital continue to cast shadows over the stock and the future of the company, which Casablanca advocates should be divided into domestic and international divisions. A featured story by Barron's earlier this afternoon took a bearish tone on Cliffs, which the publication thinks will struggle regardless of how the Casablanca story plays out.

Source: U.S. Steel website

United States Steel shed 4.6% on Friday, finishing as one of the day's worst performers for the second time this week. The company is indirectly and involuntarily in the midst of its own PR war, but its opponent is a bit more formidable than an investment bank or hedge fund. U.S. Steel has unwittingly taken center stage in a feud between the United States and China, where the U.S. has accused five members of the Chinese military of espionage and compromising the trade secrets of five American firms, including U.S. Steel. With the extent of the infiltration as yet unknown, investors have a right to be concerned. Tricks of the trade that have likely taken years to discover and millions of dollars to employ may have been surrendered permanently with a few clever strokes on the keyboard.

Finally, networking equipment manufacturer Juniper Networks tumbled 3.9% on Friday, as peer Infoblox gave the industry a scare, reporting subpar sales, and miserable projections going forward. As for Juniper, the company actually reported a long-awaited settlement with Palo Alto Networks for $750 million in cash and $100 million in equity, the results of a patent infringement lawsuit. It looks like Wall Street would've liked to see Juniper get a bit more out of the deal, but with both companies agreeing not to battle each other in the court of law for another eight years, at least there will be a guaranteed period of peace.