This is one of the disadvantages of blacklisting. The data should be accurate and checked.
In a lot of cases the actual situation has changed, but the blacklisting was not lifted.
Some scanners based on blacklists are notorious for that.
On that IP you provided, there were found instances of EXP/Pidief.aik.1, JS/Agent.cja.3, 2 instances of mdl_Phoenix exploit kit.
Status of all is dead since 2012-02-20, and the latest instance was closed 2012-02-28.
Bizimbal data: the IP Number 88.191.97.108 is not listed in Offensive IP Database.
If this is reported to avast, it will be lifted from the blacklist in one of the coming updates,