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b(b)q(ecause)g(the)f(attac)o(k)o(ers)f (knew)h(it)h(for)e(what)h(it)g(w)o(as.)146 1637 y(Of)g(late,)h(w)o(e)f(ha)o (v)o(e)g(seen)h(concerted)g(attempts)f(to)f(connect)i(to)f(random)g (addresses)h(of)f(ours.)21 b(The)75 1693 y(pattern)15 b(do)q(es)h(not)e (suggest)h(an)g(attac)o(k;)f(rather,)g(it)i(suggests)f(hosts)f(that)h(are)g (quite)h(confused)g(ab)q(out)75 1750 y(our)g(prop)q(er)g(IP)g(address.)23 b(The)16 b(problem)h(app)q(ears)f(to)f(b)q(e)i(corrupted)f(DNS)g(en)o(tries,) h(whic)o(h)g(w)o(e)e(ha)o(v)o(e)75 1806 y(also)j(exp)q(erienced,)j(rather)c (than)h(an)o(y)g(securit)o(y)g(problem.)30 b(This)18 b(problem)h(is)g (discussed)g(further)f(in)75 1863 y([Bel92].)75 1993 y Fb(2.2)56 b(Coun)n(terin)n(telligence)75 2081 y Fh(When)13 b(a)f(prob)q(e)h(o)q(ccurs,) f(w)o(e)h(try)e(to)h(learn)h(as)f(m)o(uc)o(h)g(ab)q(out)h(the)f(originating)h (mac)o(hine)g(and)g(user)f(as)g(w)o(e)75 2138 y(can.)21 b(Th)o(us)16 b(far,)e(the)i(only)g(generally-a)o(v)m(ailable)j(mec)o(hanism)d(to)f(do)g 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b(particular)h(prob)q(e)g(turned)g(out)f(to)h (b)q(e)g(an)g(exp)q(erimen)o(t)g(b)o(y)g(a)f(friend.\))20 b(T)l(o)75 2591 y(b)q(e)c(sure,)f(securit)o(y-conscious)i(sites)e(are)g(probably)h(the)g (least-lik)o(ely)h(to)e(b)q(e)h(p)q(enetrated.)k(But)c(no)f(one)75 2647 y(is)j(imm)o(une;)i(one)e(of)f(our)h(o)o(wn)f(theoretically-secure)j (gatew)o(a)o(ys)c(w)o(as)h(successfully)j(attac)o(k)o(ed)c(o)o(v)o(er)h(a)75 2704 y(w)o(eek)o(end,)e(due)h(to)f(op)q(erator)f(error.)p eop %%Page: 7 7 6 bop 146 49 a Fh(Some)18 b(sites)h(tak)o(e)f(their)i(o)o(wn)e(securit)o(y)h (precautions.)31 b(One)19 b(\(unsolicited\))i(prob)q(er)e(noticed)g(our)75 106 y(rev)o(erse)c Fc(finger)f Fh(attempt,)g(and)i(congratulated)f(us)g(on)g (it.)20 b(Others)c(who)f(though)o(t)f(w)o(e)h(w)o(ere)g(running)75 162 y(a)k(\\crac)o(k)o(er)f(c)o(hallenge)j(con)o(test")e(w)o(ere)g(able)h(to) f(detect)g(our)g(activities)i(when)f(sp)q(eci\014cally)i(lo)q(oking)75 219 y(for)17 b(them.)26 b(The)18 b(w)o(orst)e(p)q(ossibilit)o(y)j(w)o(ould)f (b)q(e)g(an)f(activ)o(e)h(resp)q(onse)g(to)e(our)h(prob)q(e;)i(it)f(could)g (easily)75 275 y(trigger)e(a)g(recursiv)o(e)i Fc(finger)p Fh(ing)e(con)o (test.)24 b(F)l(or)16 b(this)h(reason,)f(among)g(others,)g(w)o(e)h(do)f(not)g (curren)o(tly)75 332 y(do)i(rev)o(erse)h Fc(finger)p Fh(s)e(in)j(resp)q(onse) f(to)e Fc(finger)h Fh(queries,)i(but)e(the)h(problem)g(could)h(still)g (arise.)30 b(F)l(or)75 388 y(example,)14 b(an)f Fc(rusers)g Fh(query)g(to)g(us)g(w)o(ould)h(trigger)e(the)i Fc(portmopper)p Fh('s)d(coun)o(terin)o(telligence)16 b(prob)q(es;)75 444 y(these)d(in)h(turn) g(could)g(cause)f(the)h(remote)e(site)i(to)e(query)i(our)f Fc(rusers)f Fh(daemon.)19 b(It)13 b(ma)o(y)g(b)q(e)h(necessary)75 501 y(to)h(add)g(some)g(lo)q(c)o(king)h(to)f(our)g(daemons.)146 559 y(W)l(e)f(ha)o(v)o(e)h(con)o(templated)g(adding)h(other)e(arro)o(ws)f(to) i(our)f(coun)o(terin)o(telligence)k(quiv)o(er,)d(but)g(there)75 615 y(are)21 b(few)g(c)o(hoices)h(a)o(v)m(ailable.)40 b(The)22 b Fc(rusers)e Fh(command)h(is)h(an)f(ob)o(vious)h(p)q(ossibilit)o(y)l(,)j (but)c(it)h(o\013ers)75 672 y(less)c(information)f(than)h Fc(finger)e Fh(do)q(es.)27 b(T)l(o)17 b(b)q(e)h(sure,)f(b)q(ecause)i(it)e(go)q(es)g (through)g(the)h Fc(portmapper)p Fh(,)75 728 y(it)i(is)g(harder)g(to)f(blo)q (c)o(k)h(or)f(monitor;)i(unfortunately)l(,)g(man)o(y)e(sites)h(blo)q(c)o(k)g (all)h(outside)f(calls)h(to)e(the)75 785 y Fc(portmapper)f Fh(b)q(ecause)j(of)e(\(v)m(alid\))i(concerns)g(ab)q(out)e(the)h(securit)o(y)g (of)g(some)f(RPC-based)h(services.)75 841 y(Another)14 b(c)o(hoice)i(w)o (ould)f(b)q(e)g(the)g(Authen)o(tication)g(Serv)o(er[Joh85)o(],)f(but)h(our)f (exp)q(erimen)o(ts)i(sho)o(w)e(that)75 898 y(v)o(ery)k(few)g(sites)g(supp)q (ort)g(it.)29 b(And)19 b(SNMP[CFSD90)n(])f(is)h(generally)g(implemen)o(ted)h (on)e(routers,)f(not)75 954 y(hosts.)146 1012 y(A)f(totally)g(di\013eren)o(t) 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