+Add usermode +q which requires users /msg'ing or /notice'ing you to be in at least one common channel.
+This is designed to stop the spam bots which sit outside a channel, while a spy sits inside, preventing channel operators dealing with the problem.
+We currently also block invites, this might not be such a good idea, but these days everyone can get Q.
+
+diff -r f2182ca2442a include/channel.h
+--- a/include/channel.h Sun Jan 11 22:53:16 2009 +0000
++++ b/include/channel.h Sun Jan 11 22:54:00 2009 +0000
+@@ -462,5 +462,6 @@
+ extern void free_ban(struct Ban *ban);
+
+ extern unsigned int get_channel_marker(void);
++extern int common_chan_count(struct Client *a, struct Client *b, int max);
+
+ #endif /* INCLUDED_channel_h */
+diff -r f2182ca2442a include/client.h
+--- a/include/client.h Sun Jan 11 22:53:16 2009 +0000
++++ b/include/client.h Sun Jan 11 22:54:00 2009 +0000
+@@ -90,7 +90,7 @@
+ #define FlagClr(set,flag) ((set)->bits[FLAGSET_INDEX(flag)] &= ~FLAGSET_MASK(flag))
+
+ /** String containing valid user modes, in no particular order. */
+-#define infousermodes "dioOswkgxRXInP"
++#define infousermodes "dioOswkgxRXInPq"
+
+ /** Character to indicate no oper name available */
+ #define NOOPERNAMECHARACTER '-'
+@@ -192,7 +192,8 @@
+ FLAG_NOIDLE, /**< user's idletime is hidden */
+ FLAG_XTRAOP, /**< oper has special powers */
+ FLAG_OPERNAME, /**< Server sends oper name in mode string */
+-
++ FLAG_COMMONCHANSONLY, /**< SNIRCD_q: hide privmsgs/notices if in no
++ common channels (with +ok exceptions) */
+ FLAG_LAST_FLAG, /**< number of flags */
+ FLAG_LOCAL_UMODES = FLAG_LOCOP, /**< First local mode flag */
+ FLAG_GLOBAL_UMODES = FLAG_OPER /**< First global mode flag */
+@@ -622,6 +623,8 @@
+ #define IsParanoid(x) HasFlag(x, FLAG_PARANOID)
+ /** Return non-zero if the server should send opername information */
+ #define IsSendOperName(x) HasFlag(x, FLAG_OPERNAME)
++/** Return non-zero if the client has set mode +q (common chans only). */
++#define IsCommonChansOnly(x) HasFlag(x, FLAG_COMMONCHANSONLY)
+
+ /** Return non-zero if the client has operator or server privileges. */
+ #define IsPrivileged(x) (IsAnOper(x) || IsServer(x))
+@@ -685,6 +688,8 @@
+ #define SetAccountOnly(x) SetFlag(x, FLAG_ACCOUNTONLY)
+ /** Mark a client as having mode +P (paranoid). */
+ #define SetParanoid(x) SetFlag(x, FLAG_PARANOID)
++/** Mark a client as having mode +q (common chans only). */
++#define SetCommonChansOnly(x) SetFlag(x, FLAG_COMMONCHANSONLY)
+
+ /** Return non-zero if \a sptr sees \a acptr as an operator. */
+ #define SeeOper(sptr,acptr) (IsAnOper(acptr) && (HasPriv(acptr, PRIV_DISPLAY) \
+@@ -730,6 +735,8 @@
+ #define ClearAccountOnly(x) ClrFlag(x, FLAG_ACCOUNTONLY)
+ /** Remove mode +P (paranoid) from a client */
+ #define ClearParanoid(x) ClrFlag(x, FLAG_PARANOID)
++/** Remove mode +q (common chans only) from a client */
++#define ClearCommonChansOnly(x) ClrFlag(x, FLAG_COMMONCHANSONLY)
+
+ /* free flags */
+ #define FREEFLAG_SOCKET 0x0001 /**< socket needs to be freed */
+diff -r f2182ca2442a include/numeric.h
+--- a/include/numeric.h Sun Jan 11 22:53:16 2009 +0000
++++ b/include/numeric.h Sun Jan 11 22:54:00 2009 +0000
+@@ -420,6 +420,7 @@
+ /* ERR_HTMDISABLED 486 unreal */
+ #define ERR_ACCOUNTONLY 486 /* QuakeNet/ASUKA extension */
+ /* ERR_CHANTOORECENT 487 IRCnet extension (?) */
++#define ERR_COMMONCHANSONLY 487 /* QuakeNet/snircd extension */
+ /* ERR_TSLESSCHAN 488 IRCnet extension (?) */
+ #define ERR_VOICENEEDED 489 /* Undernet extension */
+
+diff -r f2182ca2442a ircd/channel.c
+--- a/ircd/channel.c Sun Jan 11 22:53:16 2009 +0000
++++ b/ircd/channel.c Sun Jan 11 22:54:00 2009 +0000
+@@ -3801,3 +3801,39 @@
+
+ return marker;
+ }
++
++/* Returns the number of common channels between two users, upto max. */
++int common_chan_count(struct Client *a, struct Client *b, int max)
++{
++ int count = 0;
++ struct Membership *cptr;
++ struct User *ua, *ub;
++ unsigned int marker = get_client_marker();
++
++ ua = cli_user(a);
++ ub = cli_user(b);
++
++ /* makes no difference to the big O complexity I know */
++ if(ua->joined > ub->joined)
++ {
++ struct User *swapee = ua;
++ ua = ub;
++ ub = swapee;
++ }
++
++ for (cptr=ua->channel;cptr;cptr=cptr->next_channel)
++ {
++ cptr->channel->marker = marker;
++ }
++
++ for (cptr=ub->channel;cptr;cptr=cptr->next_channel)
++ {
++ if (cptr->channel->marker == marker) {
++ count++;
++ if (max && (count >= max))
++ return count;
++ }
++ }
++
++ return count;
++}
+diff -r f2182ca2442a ircd/ircd_relay.c
+--- a/ircd/ircd_relay.c Sun Jan 11 22:53:16 2009 +0000
++++ b/ircd/ircd_relay.c Sun Jan 11 22:54:00 2009 +0000
+@@ -308,6 +308,10 @@
+ if (IsAccountOnly(acptr) && !IsAccount(sptr) && !IsXtraOp(sptr))
+ return;
+
++ /* slug: same applies here, since only opers can be +k */
++ if (IsCommonChansOnly(acptr) && !IsXtraOp(sptr) && !common_chan_count(acptr, sptr, 1))
++ return;
++
+ if (!(is_silenced(sptr, acptr)))
+ sendcmdto_one(sptr, CMD_PRIVATE, acptr, "%s :%s", name, text);
+ }
+@@ -360,6 +364,9 @@
+ if (IsAccountOnly(acptr) && !IsAccount(sptr) && !IsXtraOp(sptr))
+ return;
+
++ if (IsCommonChansOnly(acptr) && !IsXtraOp(sptr) && !common_chan_count(acptr, sptr, 1))
++ return;
++
+ if (!(is_silenced(sptr, acptr)))
+ sendcmdto_one(sptr, CMD_NOTICE, acptr, "%s :%s", name, text);
+ }
+@@ -399,6 +406,11 @@
+ return;
+ }
+
++ if (IsCommonChansOnly(acptr) && !IsXtraOp(sptr) && !common_chan_count(acptr, sptr, 1)) {
++ send_reply(sptr, ERR_COMMONCHANSONLY, cli_name(acptr));
++ return;
++ }
++
+ /*
+ * send away message if user away
+ */
+@@ -443,6 +455,9 @@
+ if (IsAccountOnly(acptr) && !IsAccount(sptr) && !IsXtraOp(sptr))
+ return;
+
++ if (IsCommonChansOnly(acptr) && !IsXtraOp(sptr) && !common_chan_count(acptr, sptr, 1))
++ return;
++
+ /*
+ * deliver the message
+ */
+diff -r f2182ca2442a ircd/m_invite.c
+--- a/ircd/m_invite.c Sun Jan 11 22:53:16 2009 +0000
++++ b/ircd/m_invite.c Sun Jan 11 22:54:00 2009 +0000
+@@ -171,6 +171,9 @@
+ return 0;
+ }
+
++ if (IsCommonChansOnly(acptr) && !IsXtraOp(sptr) && !common_chan_count(acptr, sptr, 1))
++ return;
++
+ if (check_target_limit(sptr, acptr, cli_name(acptr), 0))
+ return 0;
+
+diff -r f2182ca2442a ircd/s_err.c
+--- a/ircd/s_err.c Sun Jan 11 22:53:16 2009 +0000
++++ b/ircd/s_err.c Sun Jan 11 22:54:00 2009 +0000
+@@ -1006,7 +1006,7 @@
+ /* 486 */
+ { ERR_ACCOUNTONLY, "%s :You must be authed in order to message this user -- For details of how to obtain an account visit %s", "486" },
+ /* 487 */
+- { 0 },
++ { ERR_COMMONCHANSONLY, "%s :You must share at least one channel with this user in order to message them", "487" },
+ /* 488 */
+ { 0 },
+ /* 489 */
+diff -r f2182ca2442a ircd/s_user.c
+--- a/ircd/s_user.c Sun Jan 11 22:53:16 2009 +0000
++++ b/ircd/s_user.c Sun Jan 11 22:54:00 2009 +0000
+@@ -546,7 +546,8 @@
+ { FLAG_NOCHAN, 'n' },
+ { FLAG_NOIDLE, 'I' },
+ { FLAG_SETHOST, 'h' },
+- { FLAG_PARANOID, 'P' }
++ { FLAG_PARANOID, 'P' },
++ { FLAG_COMMONCHANSONLY, 'q' }
+ };
+
+ /** Length of #userModeList. */
+@@ -856,7 +857,9 @@
+ send_reply(source, ERR_ACCOUNTONLY, cli_name(source), feature_str(FEAT_URLREG));
+ return 0;
+ }
+-
++
++ /* No check here for IsCommonChansOnly since by definition we share at least one! */
++
+ if (is_notice)
+ sendcmdto_one(source, CMD_NOTICE, dest, "%C :%s", dest, text);
+ else
+@@ -1428,6 +1431,12 @@
+ else
+ ClearParanoid(sptr);
+ break;
++ case 'q':
++ if (what == MODE_ADD)
++ SetCommonChansOnly(sptr);
++ else
++ ClearCommonChansOnly(sptr);
++ break;
+ case 'r':
+ if ((what == MODE_ADD) && *(p + 1)) {
+ account = *(++p);