The ledger is a messy place full of unwanted transactions and spam. To avoid being spammed with low value transactions containing unsolicitied memos you may install a Firewall hook on your account.
Hook setup options
Allowed types
Types of transactions to allow in or out of your account (Payment, Escrow, PayChannel etc.)
Allow minimum drops
Allow a minimum number of drops for an incoming txn to be allowed.
Trustline minimums
Allow a minimum amount to be specified for each of the trustline assets on the account.
Memo max size
Allow any txn with a memo larger than X bytes to be blocked regardless of other rules.
More Hooks
Savings
Save a predefined amount to savings account from transactions of your choice.
Blocklist
Filter outgoing and incoming payments against a known list of scam accounts.
Direct Debit
Allow trusted third parties to pull funds from your account up to a limit you set.
Payment Watchdog
Get notified before sending high value transactions out of your account