When I started getting spam on my website (which did not take long at all!), I discovered that Akismet must be enabled before it will work (obvious yes, but it didn’t occur to me when I first installed WordPress).
I am very glad I enabled it! Since being away from the Internet for a while (one week), Akismet has caught 68 spam comments!
It is good to be on the Internet radar, but with this comes problems, like spam. I highly recommend Akismet to drastically reduce this problem!