Recent public prosecutions, parliamentary testimony and statements by security-service chiefs suggest that, outside declared liaison channels, somewhere between roughly 7,000 and 16,000 human sources are today spying against the ten most-targeted countries.
The lower bound starts from what the FBI calls "a new China-related counterintelligence case every 10 hours" and MI5's warning that "an estimated 20,000 Britons have been approached" by Chinese collectors, then strips out non-HUMINT cases and over-counted investigations.12 The upper bound assumes undetected-spy ratios of about four-to-one applied to these baselines and to Europe's post-Ukraine "expulsion of some 600 Russian diplomats."3
The United States and Russia face the deepest penetration (low thousands each), while middle-tier states such as Iran and Israel confront only dozens to low hundreds but feel every loss acutely.
All numbers below combine what is openly admitted (arrests, expulsions, case totals) with conservative dark-figure multipliers to reflect undetected assets.
Summing these mid‑range estimates gives roughly 11,000 currently active human sources. Applying the ±40% uncertainty range yields an aggregate span of about 7,000–16,000 live assets, not counting declared liaison channels or short‑term battlefield informants.
Methodology
Only figures traceable to court documents, parliamentary transcripts or official press conferences are used. The FBI's China caseload, MI5's LinkedIn outreach numbers and BfV's public annual report are treated as rough stocks of known or suspected foreign agents, not as full universe counts.123 Arrest totals are aggregated for 2015-25 to smooth annual spikes tied to specific wars, expulsions or legislative changes.
Academic and practitioner studies of post-arrest debriefs typically put undetected-spy ratios between 3:1 and 10:1. To stay conservative, the table uses a core dark-figure multiplier of x4, except where a service publishes its own claimed network size (as Iran does with the "identify 290 CIA spies in Iran" announcement, or the FBI with its ~5,000 CI cases).1[^13] A ±40% uncertainty band is then applied to yield the low-high ranges.
Diplomat expulsions and mass outreach campaigns provide independent sanity checks. BfV ties Russia's recent recruitment push directly to "expulsion of some 600 Russian diplomats" across Europe,3 while MI5 highlights both the scale ("an estimated 20,000 Britons have been approached") and the low conversion rate of Chinese LinkedIn trawling.2 If only a fraction of those approached are turned, this still easily supports the order-of-magnitude estimates for UK and EU cases.
Diplomat expulsions (600 Russian officials from Europe, half assessed as intelligence officers)16 and MI5's 20,000 Chinese LinkedIn approaches provide independent sanity tests for the multipliers.