diff --git a/check_csgo/check_csgo.cpp b/check_csgo/check_csgo.cpp
index 28ba4a2..e97d910 100644
--- a/check_csgo/check_csgo.cpp
+++ b/check_csgo/check_csgo.cpp
@@ -1,164 +1,166 @@
 #include "check_csgo.h"
+#include <vector>
 
 using namespace std;
 
 char *servicename = (char*)"CS:GO";
 
-void printVersion()
-{
-	cout << "check_csgo v" << VERSION << endl << endl;
+void printVersion() {
+  cout << "check_csgo v" << VERSION << endl << endl;
 }
 
-void printHelp(bool longVersion)
-{
-	if(longVersion)
-	{
-		printVersion();
-		cout << "Check CS:GO DS instance." << endl << endl;
-		printHelp(false);
-		cout << "Options:" << endl;
-		cout << " -h" << endl;
-		cout << "    Print detailed help screen" << endl;
-		cout << " -V" << endl;
-		cout << "    Print version information" << endl;
-		cout << " -H HOSTADDRESS" << endl;
-		cout << "    Host where the Source DS is running" << endl;
-		cout << " -p" << endl;
-		cout << "    Port where the Source DS is listening. Default is 27015." << endl << endl;
-		return;
-	}
-	cout << "Usage: " << endl << "check_csgo [-hV] -H HOSTADDRESS [-p PORT]" << endl << endl;
+void printHelp(bool longVersion) {
+  if(longVersion) {
+    printVersion();
+    cout << "Check CS:GO DS instance." << endl << endl;
+    printHelp(false);
+    cout << "Options:" << endl;
+    cout << " -h" << endl;
+    cout << "    Print detailed help screen" << endl;
+    cout << " -V" << endl;
+    cout << "    Print version information" << endl;
+    cout << " -H HOSTADDRESS" << endl;
+    cout << "    Host where the Source DS is running" << endl;
+    cout << " -p" << endl;
+    cout << "    Port where the Source DS is listening. Default is 27015." << endl << endl;
+    return;
+  }
+  cout << "Usage: " << endl << "check_csgo [-hV] -H HOSTADDRESS [-p PORT]" << endl << endl;
 }
 
-SOURCEDS_PACKET* getSourceDSResponse(int s, sockaddr_in *server)
-{
-    char *data = new char[DATAGRAM_LENGTH];
-    int dataLength = recvMsg(s, data, DATAGRAM_LENGTH, server);
-    if(dataLength == -1)
-    {
-        return NULL;
-    }
-    char *header = (char*) "\xFF\xFF\xFF\xFF";
-    if(memcmp(data,header,HDR_SIZE))
-    {
-       //Invalid response, or non-supported multi-packet response format
-       return NULL;
-    }
-    SOURCEDS_PACKET *response = new SOURCEDS_PACKET;
-    response->data = data+HDR_SIZE;
-    response->length = dataLength;
-    return response;
+SOURCEDS_PACKET* getSourceDSResponse(int s, sockaddr_in *server) {
+  char *data = new char[DATAGRAM_LENGTH];
+  int dataLength = recvMsg(s, data, DATAGRAM_LENGTH, server);
+  if(dataLength == -1) {
+    return NULL;
+  }
+  char *header = (char*) "\xFF\xFF\xFF\xFF";
+  if(memcmp(data,header,HDR_SIZE)) {
+    //Invalid response, or non-supported multi-packet response format
+    return NULL;
+  }
+  SOURCEDS_PACKET *response = new SOURCEDS_PACKET;
+  response->data = data+HDR_SIZE;
+  response->length = dataLength;
+  return response;
 }
 
-int check_csgo(char *hostname, uint16_t port, SERVERINFO *server_info)
-{
-    struct sockaddr_in si;
-    struct hostent *host = NULL;
-    int s;
-    int timeout = 10;
-    setupSocket(port,hostname,host,timeout,&si,&s);
-    string discard;
-
-    char *info_query = (char*) "\xFF\xFF\xFF\xFF\x54Source Engine Query\x00";
-
-    sendMsg(s,info_query, strlen(info_query)+1,&si);
-    SOURCEDS_PACKET *response = getSourceDSResponse(s,&si);
-    if(response == NULL)
-    {
-        return 2;
-    }
-
-    ssize_t offset = 2;
-    server_info->name = string(response->data+offset,strlen(response->data+offset));
-    offset += server_info->name.size()+1;
-    server_info->map = string(response->data+offset,strlen(response->data+offset));
-    offset += server_info->map.size()+1;
-    discard = string(response->data+offset,strlen(response->data+offset));
-    offset += discard.size() + 1;
-    server_info->game = string(response->data+offset,strlen(response->data+offset));
-    offset += server_info->game.size()+1;
-    offset += 2;
-    server_info->players = (uint8_t) *((response->data)+offset);
-	server_info->max_players = (uint8_t) *((response->data)+(++offset));
-
+int check_csgo(char *hostname, uint16_t port, SERVERINFO *server_info) {
+  struct sockaddr_in si;
+  struct hostent *host = NULL;
+  int s;
+  int timeout = 10;
+  setupSocket(port,hostname,host,timeout,&si,&s);
+  string discard;
+
+  std::vector<uint8_t> info_query;
+  info_query.resize(25);
+  memcpy(info_query.data(), "\xFF\xFF\xFF\xFF\x54Source Engine Query\x00", 25);
+
+  sendMsg(s, reinterpret_cast<char*>(info_query.data()), info_query.size(), &si);
+  SOURCEDS_PACKET *response = getSourceDSResponse(s,&si);
+  if(response == NULL) {
+    return 2;
+  }
+
+  if(response->data[0] == 'A') {
+    // Challenge response mechanism
+    uint32_t challenge;
+    size_t current_pkt_size = info_query.size();
+    info_query.resize(current_pkt_size + 4);
+    memcpy(info_query.data() + current_pkt_size, response->data+1, 4);
     delete[] (response->data-HDR_SIZE);
     delete response;
 
-    if(server_info->players == server_info->max_players)
-    {
-        return 1;
+    sendMsg(s, reinterpret_cast<char*>(info_query.data()), info_query.size(), &si);
+    response = getSourceDSResponse(s, &si);
+    if(response == NULL) {
+      return 2;
     }
-
-    return 0;
+  }
+
+  ssize_t offset = 2;
+  server_info->name = string(response->data+offset,strlen(response->data+offset));
+  offset += server_info->name.size()+1;
+  server_info->map = string(response->data+offset,strlen(response->data+offset));
+  offset += server_info->map.size()+1;
+  discard = string(response->data+offset,strlen(response->data+offset));
+  offset += discard.size() + 1;
+  server_info->game = string(response->data+offset,strlen(response->data+offset));
+  offset += server_info->game.size()+1;
+  offset += 2;
+  server_info->players = (uint8_t) *((response->data)+offset);
+  server_info->max_players = (uint8_t) *((response->data)+(++offset));
+
+  delete[] (response->data-HDR_SIZE);
+  delete response;
+
+  if(server_info->players == server_info->max_players) {
+    return 1;
+  }
+
+  return 0;
 }
 
-int main(int argc, char **argv)
-{
-	struct itimerval timer;
-	timer.it_value.tv_sec = 10;
-	timer.it_value.tv_usec = 0;
-	timer.it_interval.tv_sec = 0;
-	timer.it_interval.tv_usec = 0;
-	setitimer (ITIMER_VIRTUAL, &timer, 0);
-
-	struct sigaction sa;
-	memset (&sa, 0, sizeof (sa));
-	sa.sa_handler = &timer_handler;
-	sigaction (SIGVTALRM, &sa, 0);
-
-	uint16_t port = 27015;
-	char *hostname = NULL;
-	int c;
-
-	while ((c = getopt (argc, argv, "H:p:Vh")) != -1)
-	{
-		switch(c)
-		{
-			case 'H':
-        			hostname = optarg;
-        			break;
-			case 'p':
-       		 		port = (uint16_t) str2int(optarg);
-       		 		break;
-			case 'V':
-				printVersion();
-				return 0;
-			case 'h':
-				printHelp(true);
-				return 0;
-			case '?':
-				printHelp(false);
-				return 3;
-		}
-	}
-
-	if(hostname == NULL)
-	{
-		cout << "No HOSTADDRESS specified. Exiting." << endl;
-		return 3;
-	}
-
-	SERVERINFO server_info;
-	int returnCode = check_csgo(hostname,port,&server_info);
-
-	cout << servicename;
-	switch(returnCode)
-	{
-		case 0:
-			cout << " OK";
-            cout << " - " << hostname << " " << server_info.name << " " << server_info.game << " " << server_info.map
-                 << " " << (int)server_info.players << "/" << (int)server_info.max_players << " players" << endl ;
-			break;
-
-        case 1:
-            cout << " WARNING - Server is full";
-            break;
-
-		case 2:
-			cout << " CRITICAL - No response";
-			break;
-	}
-
-
-	return returnCode;
+int main(int argc, char **argv) {
+  struct itimerval timer;
+  timer.it_value.tv_sec = 10;
+  timer.it_value.tv_usec = 0;
+  timer.it_interval.tv_sec = 0;
+  timer.it_interval.tv_usec = 0;
+  setitimer (ITIMER_VIRTUAL, &timer, 0);
+
+  struct sigaction sa;
+  memset (&sa, 0, sizeof (sa));
+  sa.sa_handler = &timer_handler;
+  sigaction (SIGVTALRM, &sa, 0);
+
+  uint16_t port = 27015;
+  char *hostname = NULL;
+  int c;
+
+  while ((c = getopt (argc, argv, "H:p:Vh")) != -1) {
+    switch(c) {
+      case 'H':
+        hostname = optarg;
+        break;
+      case 'p':
+        port = (uint16_t) str2int(optarg);
+       	break;
+      case 'V':
+        printVersion();
+        return 0;
+      case 'h':
+        printHelp(true);
+        return 0;
+      case '?':
+        printHelp(false);
+        return 3;
+    }
+  }
+
+  if(hostname == NULL) {
+    cout << "No HOSTADDRESS specified. Exiting." << endl;
+    return 3;
+  }
+
+  SERVERINFO server_info;
+  int returnCode = check_csgo(hostname,port,&server_info);
+
+  cout << servicename;
+  switch(returnCode) {
+    case 0:
+      cout << " OK";
+      cout << " - " << hostname << " " << server_info.name << " " << server_info.game << " " << server_info.map
+           << " " << (int)server_info.players << "/" << (int)server_info.max_players << " players" << endl ;
+      break;
+
+    case 1:
+      cout << " WARNING - Server is full";
+      break;
+    case 2:
+      cout << " CRITICAL - No response";
+      break;
+  }
+  return returnCode;
 }