Theia
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Overview
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Theia is the worlds first FOSS malware scanner for Android. It is powered by ClamAV signature databases (GPLv3).

Features
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- Near zero battery impact: you'll never notice any impact on battery at all
- Extremely fast: it can scan small files (1MB) in <20ms, and even large files (40MB) in 1000ms.
- Memory efficient: with the default databases enabled it uses under 120MB.
- Regular scan: allowing selection of /system, internal storage, external storage, and installed apps
- Realtime scanner: can detect malware in realtime on write/rename in internal storage
- Completely offline: Internet is only used to download signature databases, files will never ever leave your device
- Tiny codebase: coming in at under 1000 sloc, it can be audited by even someone with basic programming experience
- Minimal dependencies: the app only uses libraries when necessary
- Signature databases can be enabled/disabled at the users demand

Technical Details
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- Signature databases are ClavAV .hdb (MD5 hashes) and .hsb (SHA-1/SHA-256) format
- Signature databases will not be redownloaded if the file hasn't changed on the server (304 not modified)
- Realtime scanning powered by recursive FileObserver (Credit: @iNPUTmice)
- Signatures are stored using HashMaps for O(1) lookup
- Files have their MD5/SHA-1/SHA-256 hashes calculated in one pass

Credits
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- Trove (GPLv3): A memory efficient replacement for Java's Collections
- RecursiveFileObserver.java (GPLv3): Daniel Gultsch, ownCloud Inc., Bartek Przybylski
- Icons (Apache-2.0): Google/Android/AOSP