Put the summary of the bug you're having here

*MC launches until it gives blank white screen "update notes" and the option "play offline" is tabbed at bottom. Upon selection, portal to app appears, select "singleplayer" brings up "select world" Select "builds" then "play selected world" crashes app with note: "Java.lang.Illegalstateexception: failed to create a child event loop"

The error message tracks the kinds of error messages received with Avast security software problem that I've seen here, though that is not loaded on platform.

Note: issue started after son accidently downloaded expertpdf7.exe, catW adware, and folder Arcade Patrol. Don't ask. Collateral problem was that web pages wouldn't load. Removed all adware fixing webpage loading problem, but not MC launching problem. However, execution of MC app and crash brings up similar message after deletion of adware files regarding adware dll file which cannot be found. The question is, why was MC app looking for it? I suppose. Reinstalled java (64 bit)

---- Minecraft Crash Report ----
// Sorry

Time: 3/16/15 4:48 AM
Description: Updating screen events

java.lang.IllegalStateException: failed to create a child event loop
at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:68)
at io.netty.channel.MultithreadEventLoopGroup.<init>(MultithreadEventLoopGroup.java:49)
at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:61)
at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:52)
at lm$1.a(SourceFile:44)
at lm$1.b(SourceFile:41)
at np.c(SourceFile:10)
at lm.a(SourceFile:121)
at avf.a(SourceFile:1941)
at axw.i(SourceFile:172)
at axw.a(SourceFile:135)
at axv.a(SourceFile:350)
at axv.k(SourceFile:413)
at axw.k(SourceFile:81)
at axv.p(SourceFile:390)
at avf.s(SourceFile:1497)
at avf.av(SourceFile:888)
at avf.a(SourceFile:325)
at net.minecraft.client.main.Main.main(SourceFile:124)
Caused by: io.netty.channel.ChannelException: failed to open a new selector
at io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:128)
at io.netty.channel.nio.NioEventLoop.<init>(NioEventLoop.java:120)
at io.netty.channel.nio.NioEventLoopGroup.newChild(NioEventLoopGroup.java:87)
at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:64)
... 18 more
Caused by: java.io.IOException: Unable to establish loopback connection
at sun.nio.ch.PipeImpl$Initializer.run(Unknown Source)
at sun.nio.ch.PipeImpl$Initializer.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at sun.nio.ch.PipeImpl.<init>(Unknown Source)
at sun.nio.ch.SelectorProviderImpl.openPipe(Unknown Source)
at java.nio.channels.Pipe.open(Unknown Source)
at sun.nio.ch.WindowsSelectorImpl.<init>(Unknown Source)
at sun.nio.ch.WindowsSelectorProvider.openSelector(Unknown Source)
at io.netty.channel.nio.NioEventLoop.openSelector(NioEventLoop.java:126)
... 21 more
Caused by: java.net.SocketException: Unrecognized Windows Sockets error: 10106: socket
at sun.nio.ch.Net.socket0(Native Method)
at sun.nio.ch.Net.serverSocket(Unknown Source)
at sun.nio.ch.ServerSocketChannelImpl.<init>(Unknown Source)
at sun.nio.ch.SelectorProviderImpl.openServerSocketChannel(Unknown Source)
at java.nio.channels.ServerSocketChannel.open(Unknown Source)
at sun.nio.ch.PipeImpl$Initializer$LoopbackConnector.run(Unknown Source)
... 30 more

A detailed walkthrough of the error, its code path and all known details is as follows:
---------------------------------------------------------------------------------------

– Head –
Stacktrace:
at io.netty.util.concurrent.MultithreadEventExecutorGroup.<init>(MultithreadEventExecutorGroup.java:68)
at io.netty.channel.MultithreadEventLoopGroup.<init>(MultithreadEventLoopGroup.java:49)
at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:61)
at io.netty.channel.nio.NioEventLoopGroup.<init>(NioEventLoopGroup.java:52)
at lm$1.a(SourceFile:44)
at lm$1.b(SourceFile:41)
at np.c(SourceFile:10)
at lm.a(SourceFile:121)
at avf.a(SourceFile:1941)
at axw.i(SourceFile:172)
at axw.a(SourceFile:135)
at axv.a(SourceFile:350)
at axv.k(SourceFile:413)
at axw.k(SourceFile:81)
at axv.p(SourceFile:390)

– Affected screen –
Details:
Screen name: ayb
Stacktrace:
at avf.s(SourceFile:1497)
at avf.av(SourceFile:888)
at avf.a(SourceFile:325)
at net.minecraft.client.main.Main.main(SourceFile:124)

– System Details –
Details:
Minecraft Version: 1.8.3
Operating System: Windows 8.1 (x86) version 6.3
CPU: 4x Intel(R) Core(TM) i5-4200U CPU @ 1.60GHz
Java Version: 1.8.0_40, Oracle Corporation
Java VM Version: Java HotSpot(TM) Client VM (mixed mode), Oracle Corporation
Memory: 107865432 bytes (102 MB) / 230526976 bytes (219 MB) up to 523501568 bytes (499 MB)
JVM Flags: 6 total; -XX:HeapDumpPath=MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump -Xmx512M -XX:+UseConcMarkSweepGC -XX:+CMSIncrementalMode -XX:-UseAdaptiveSizePolicy -Xmn128M
IntCache: cache: 0, tcache: 0, allocated: 0, tallocated: 0
Launched Version: 1.8.3
LWJGL: 2.9.4
OpenGL: Intel(R) HD Graphics 4400 GL version 4.2.0 - Build 10.18.10.3304, Intel
GL Caps: Using GL 1.3 multitexturing.
Using GL 1.3 texture combiners.
Using framebuffer objects because OpenGL 3.0 is supported and separate blending is supported.
Shaders are available because OpenGL 2.1 is supported.
VBOs are available because OpenGL 1.5 is supported.

Using VBOs: No
Is Modded: Probably not. Jar signature remains and client brand is untouched.
Type: Client (map_client.txt)
Resource Packs: []
Current Language: English (US)
Profiler Position: N/A (disabled)