Browser bookmark altered by undetected intruder?

I site I visit regularly was subjected to a ddos attach yesterday - I couln't reach the site this morning via my browser bookmark button - got a page unresponsive message.  I noticed that the url looked odd - the .com portion of the address was missing and appeared to have been replaced with two forward slashes ("//").  Did a search for the website (duckduckgo) and copied and pasted the address into a new browser window, reached the site successfully.  There I learned that the site had been subjected to the ddos attack, and another user mentioned in a comment that the url he used had been changed to a "directory" - no other detail.  The nonfunctioning address was the one stored with my bookmark - checked that with a mouseover.  Is it possible that an intruder altered the address??  I thought Webroot would catch something like that.