[Bio-software] Motif Finding programs / algorithms

[mark]

Hello,

I am a new in bioinformatics field. Presently I am looking at good
description (algorithms / open software) about finding motifs for
DNA/RNA strings. I.e. my task is just to explore the problem of finding
the longest motifs (with possible mutation) in the specified number of
strings. Would be grateful for any information about that problems
(tutorials / books / source codes / descriptions / etc.).

Regards, Mark