While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a closer look at particularly stock-shaking upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Palo Alto Networks (PANW -1.71%) surged 3% today after Nomura Securities upgraded the network security technologist from neutral to buy.

So what: Along with the upgrade, analyst Frederick Grieb planted a price target of $80 on the stock, representing about 19% worth of upside to Friday's close. So while momentum traders might be turned off by Palo Alto's price weakness in recent months, Grieb's call could reflect a sense on Wall Street that its growth prospects are becoming too cheap to pass up.

Now what: According to Nomura, Palo Alto's risk/reward trade-off is rather attractive at this point. "We continue to view Palo Alto as one of the best positioned vendors in the Network Security space," Grieb said. "The company was highlighted as a top share gainer in our CSO Survey and in our recent Reseller Survey (published in April) 58% of Palo Alto resellers were ahead of plan, with just 8% behind plan. Finally, Palo Alto has also shown itself to be a fast follower (critical for Network Security companies), quickly bringing to market WildFire, which competes with FireEye in the important APT Protection market." When you couple that upbeat outlook with Palo Alto's cash-rich balance sheet, it's tough to disagree with Nomura's bullishness.