I'm not a TCP expert, but if the TCP flags are truly invalid your operating system will handle the TCP packet accordingly. Why the firewall shows those alerts in its logs I don't know.

By the way, hacking somebody, who is not running a publicly accessible server listening on some port is almost impossible.
Windows, by default, listens on the NetBIOS port, but you can trust that to be relatively secure if you turn off windows shares. If you don't run any other services like an Exchange Server, a ftp server or IIS.

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Morgens ess ich Cornflakes und abends ess ich Brot
Und wenn ich lang genug gelebt hab, dann sterb ich und bin tot

--Fischmob