Why do my transactions show I received 1 satoshi? My Multi-Bit client shows 1 satoshi sent to me in my receiving transactions, with 1 confirmation only. The receiving address is quite old too. Why is that showing up when I didn't send myself anything and no one would have any reason to send me anything?

  fc973596838c5d001efd77060c775cd85f0ac3821ae813e64116d9eb66ead30a: Seen by 1 peer. Pending/unconfirmed.
     from 1Enjoy1C4bYBr3tN4sMKxvvJDqG8NkdR4Z / 3d96dee6b4aaeeed1d5a95446c6fba4ab3ff0664aaf76773428c485d86f697fb:1
       to 1Pfe9cYYQYGbKdSddLxuFyYRmvNoFPgVWu 0.00000001 BTC
       to 1Meshuse4ZU16HjLmnUCYt3DFEHvp1qscw 0.00000001 BTC
       to 1PKE81BAg8RHYLGqLCsVcnWCspcfekokwG 0.00000001 BTC
       to 18omoJATGraMgghRrocCoSnR2gz6mx8DkW 0.00000001 BTC
       to 19qn25QVqn3ZH6UT63PbgtSBsyAgyaWxAA 0.00000001 BTC
       to 1HNyt3qg3qgL2XhhcsjMD6d9zpDB98Kqqw 0.00000001 BTC
       to 1CrRqLtF766WTAx1VEzJr9rwFWjV5xpqAX 0.00000001 BTC
       to 1D6JBqA5ixpvNS4RjthapT4c5zkut4yNf1 0.00000001 BTC
... body is limited to 30,000 characters ....
       to 17jVF27wAV9bhneRFsnLTySMUjtPWHZVwB 0.00000001 BTC
       to 1MoVuJTG4DV1r37Ew11ePWefn3uFb8vDmm 0.00000001 BTC
       to 1GBE3BrqzfevPDsSzJaJpTa1VyKMWTt5MZ 0.00000001 BTC
       to 1BMR6fDvuqPan3QA9iNUJxXeHtvLKmRaeq 0.00000001 BTC
       to 1Enjoy1C4bYBr3tN4sMKxvvJDqG8NkdR4Z 0.0000225 BTC
That particular transaction is an attempt at something that has become known as "dust spam". The idea is that the sender sends a very small amount of bitcoin to many different addresses, hoping that people will notice and investigate further. It's possible to find out who sent this if you look hard enough, but most people won't bother. The effectiveness of this kind of spam is clearly limited.

For more information, see the Reddit thread PSA: Did you receive a "dust" amount of BTC from "Enjoy" and "Sochi"? Here's why.