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Avatars:
- none (default Twitter avatar)
- professionally photographed female picture
- business logo
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Names:
- username or full name containing trailing digits
- first and last name joined without a space in between
- female porn-sounding name
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Bio:
- contains "viral", "social media", "marketing"
- website is to a business site, rather than personal
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Follow stats:
- orders of magnitude more following than followers
- followers are mostly other shady accounts (usually without avatars)
-
Tweets:
- frequent linking to a single site
- @-replying different people with the same product pitch
- each update is in form of a news headline, followed by a link
- several consecutive updates are proverbs/famous quotes
Also see: What makes you a Twitter spammer?