The problem may be that someone has found out your email address and password.
Lets say you have an email address of
[email protected] and a password of "football".
Then lets say you register with lots of web sites such as ebay, amazon, tesco etc - and on each of these you register with
[email protected] with the same password of "football".
Now lets assume you register with a slightly "dodgy" web site (not porn but maybe a less trustworthy site), and again you register with
[email protected] and password "football".
So now every time you log on to that web site you are "giving away" your email and password combination. Once you have given it away people will then try the same combination on sites like ebay, amazon and so on.
Always use a DIFFERENT password for your email address than the one you use for web sites.
Even better have 2 or 3 email addresses, and keep one for JUST valid sites like ebay, your bank etc. Use another email address for "dodgy" sites so if your details are stolen they cant get in to ebay or you bank.