It is not a problem, since Avast blocked it
And the LSASS exploit is really old.
Worms like Sasser and Blaster are using this exploit.
Just make sure you have
ALL security patches/updates installed for your system.
Nothing to worry about if you have your system up-to-date and have configured Avast and your firewall correctly.
EDIT: Make yourself familiar with the applications you use using the help files. They contain a lot of information.
Also use the search option on this board. A lot of questions have been asked and answered here.