Thousands of Wordpress hacked again?

Today I was visiting my websites and when I looked at the bottom/top of my Wordpress I found this string printed. What does this mean? I have seen posts in Wordpress forum which say that there are many sites hacked. What did the hack do on the sites?

object(core)#1 (31) {
  ["donor"]=>
  string(21) "mydomain.net/folder/"
  ["useragent"]=>
  string(109) "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/40.0.2214.115 Safari/537.36"
  ["charset"]=>
  string(5) "UTF-8"
  ["ownerid"]=>
  int(1)
  ["hash"]=>
  string(32) "b3039dd11dfdc07ede66b6141b76e894"
  ["url"]=>
  string(21) "mydomain.net/folder/"
  ["bot"]=>
  string(0) ""
  ["botId"]=>
  int(0)
  ["onlynew"]=>
  NULL
  ["y_ip"]=>
  NULL
  ["g_ip"]=>
  NULL
  ["ipuser"]=>
  NULL
  ["zone"]=>
  string(3) "net"
  ["domain"]=>
  string(14) "mydomain.net"
  ["subdomain"]=>
  string(0) ""
  ["subdomainid"]=>
  string(4) "NULL"
  ["frozen"]=>
  string(1) "0"
  ["common"]=>
  bool(false)
  ["donorid"]=>
  string(4) "2632"
  ["zoneid"]=>
  string(1) "2"
  ["securehash"]=>
  string(32) "f4c99527557520f0be883d2aafa85d40"
  ["code"]=>
  NULL
  ["showbots"]=>
  string(1) "0"
  ["randtasks"]=>
  string(1) "0"
  ["showmobile"]=>
  string(1) "0"
  ["showsearchref"]=>
  string(1) "0"
  ["urlcrc32"]=>
  NULL
  ["db":"core":private]=>
  object(PDO)#4 (0) {
  }
  ["statQueries":"core":private]=>
  array(0) {
  }
  ["mem":"core":private]=>
  object(Jamm\Memory\APCObject)#3 (9) {
    ["prefix":protected]=>
    string(36) "ic-506a02e252fa192e184ab76d57b747ec."
    ["lock_key_prefix":protected]=>
    string(46) ".lock_key.ic-506a02e252fa192e184ab76d57b747ec."
    ["defragmentation_prefix":protected]=>
    string(7) ".clean."
    ["tags_prefix":protected]=>
    string(42) ".tags.ic-506a02e252fa192e184ab76d57b747ec."
    ["key_lock_time":protected]=>
    int(30)
    ["max_wait_unlock":protected]=>
    float(1.05)
    ["last_err":"Jamm\Memory\MemoryObject":private]=>
    NULL
    ["err_log":"Jamm\Memory\MemoryObject":private]=>
    NULL
    ["errors_triggering":"Jamm\Memory\MemoryObject":private]=>
    bool(true)
  }
  ["initSqlQuery":"core":private]=>
  string(26) "set session sql_mode = "";"
}

How can I permanently solve this problem? Thanks in advance