Echofon is notifying you that a Twitter user has mentioned your twitter account in one of their own tweets. In the Twitter web interface, you would see these tweets under the "@ Connect" tab, possibly buried under the option labeled "Mentions".
There are numerous spam bots that will tweet "at" you, usually in response to one of your public tweets that mentions a keyword. As you stated, "webcam" was one that attracted the bots. Mention of various Apple Computer product names is one that I've seen attract the bots in full force.
When your public tweet brings your Twitter account to the attention of the spambots, they will react. One of the ways in which they react is to reply to your tweet or to "mention" you.
You post something like:
"My new remote controlled helicopter arrives tomorrow! Hooray!"
And the spambots respond with:
@your-twitter-account I know, right? i got mine today from (some spam
@your-twitter-account FREE HELICOPTER FOR THE FIRST TEN PEOPLE (some
Hey, I think @your-twitter-account is loving his new remote from (some
@your-twitter-acocunt @someone-else #trendinghashtag (spam link) i
blah bloop bleep
When Echofon asks Twitter for a list of your "mentions" and/or "interactions", the tweets from the spam bots are included in the list. Echofon then notifies you of these tweets.
In a world without spam, this is useful behavior. It facilitates conversations with new people who you might not have otherwise interacted with.
Echofon for iOS recently (as of May 8, 2012) gained a new feature:
- Refine push notification settings
- Added an option receiving mentions notification only from people you follow
Echofon for Windows and for Firefox do not seem to have such a feature yet.
You could request the feature be added to Echofon, you could tolerate the occasional spam notifications (and report/block the accounts), or you could find another Twitter client that has a feature to suppress notification of mentions from accounts you do not follow.
Best of luck!