MBAM checks for updates regularly when I open it to scan and should be up to date. My current version is 1.51.2.1300
default setting is to alarm if signatures is older then 7 days....you may sett it to 1 anyway i always hit the update button before i scan

you can report False Positive here
http://www.avast.com/en-us/contact-form.php?loadStyles

you may add a link to this topic

if you are still suspicious that you have something ?
you can follow this guide and attach the OTL log so essexboy can have a look…
http://forum.avast.com/index.php?topic=53253.0