My OS is Ubuntu 16.04.  I have tried to download from the Tor website and using Unbuntu's software package.  Each time I get a message titled Signature Verification Failed.  The message is: "You might be under attack, or there might just be a networking problem. Click Start try the download again."  I have tried many times, always getting the same result.  I have wiped the hard drive and reloaded Unbuntu 3 times.  I have loaded Tor on my laptop which uses the same router and Internet connection.